Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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41421 Publications

Justification of best-estimate transient calculations in comparison to the steady-state bounding-case approach

Sangiorgi, M.; Carenini, L.; Brumm, S.; Le Tellier, R.; Viot, L.; Wu, Z.; Xia, S.; Bakouta, N.; Ederli, S.; Mascari, F.; Harti, M.; Lecomte, M.; Sagan, M.; Pandazis, P.; Jobst, Matthias; Gencheva, R.; Groudev, P.; Barnak, M.; Matejovic, P.; Villanueva, W.; Chen, Y.; Ma, W.; Bechta, S.; Kaliatka, A.; Valinius, M.; Kostka, P.; Techy, Z.; Vorobyov, Y.; Thomas, R.; Vokac, P.; Kotouc, M.; Korpinen, A.; Fichot, F.

In the scope of the European IVMR (In-Vessel Melt Retention) project, calculations of In-Vessel retention (IVR) strategy with state of the art Severe Accident (SA) computer codes were performed, including the integral codes ASTEC, ATHLET-CD, MAAP, MELCOR and RELAP5/SCDAPSIM. Further codes dedicated to the study of lower plenum behaviour were also included. Simulations were performed for several types of reactors (PWR, VVER-440, VVER-1000, BWR) and several severe accident scenarios (Station Blackout (SBO) accidents and Loss-Of-Coolant accidents of several leak sizes combined with SBO). The code improvements for IVR simulation, implemented during the project, are summarized and the results obtained with the improved codes are presented in the paper.

Keywords: In-vessel melt retention; Severe Accidents; PWR; VVER-1000; VVER-440; BWR; Accident Management Measures; SBO; LOCA

  • Contribution to proceedings
    International Seminar “In-vessel retention: outcomes of IVMR project”, 20.-21.01.2020, Juan-les-Pins, France

Permalink: https://www.hzdr.de/publications/Publ-31778
Publ.-Id: 31778


Structural and magnetic properties of swift heavy-ion irradiated SiC

Zhang, X.; Zhang, Z.; Akhmadaliev, S.; Zhou, S.; Wu, Y.; Guo, B.

Ferromagnetism has been observed in ion and neutron irradiated SiC single crystals. In this paper, we present a structural and magnetic investigation on 6H–SiC irradiated by swift heavy ions. The co-exist of paramagnetism, superparamagnetism and ferromagnetism is revealed by using different magnetometry methods. The ferromagnetic component persists well above room temperature. This study confirms the general existence of defect-induced magnetism in SiC.

Keywords: Ferromagnetism Magnetometry; Heavy ions; Silicon carbide; Superparamagnetism; Ferromagnetic component; Induced magnetism; Neutron irradiated SiC single crystals; Structural and magnetic properties; Swift heavy ions; Silicon compounds

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Permalink: https://www.hzdr.de/publications/Publ-31777
Publ.-Id: 31777


Research Data for: ctmmweb: A graphical user interface for autocorrelation-informed home range estimation

Calabrese, J. M.; Fleming, C.; Noonan, M. J.; Dong, X.

Estimating animal home ranges is a primary purpose of collecting tracking data. All conventional home range estimators in widespread usage, including minimum convex polygons and kernel density estimators, assume independently sampled data. In stark contrast, modern GPS animal tracking datasets are almost always strongly autocorrelated. This incongruence between estimator assumptions and empirical reality leads to systematically underestimated home ranges. Autocorrelated kernel density estimation (AKDE) resolves this conflict by modeling the observed autocorrelation structure of tracking data during home range estimation, and has been shown to perform accurately across a broad range of tracking datasets. However, compared to conventional estimators, AKDE requires additional modeling steps and has heretofore only been accessible via the command-line ctmm R package. Here, we introduce ctmmweb, which provides a point-and-click graphical interface to ctmm, and streamlines AKDE, its prerequisite autocorrelation modeling steps, and a number of additional movement analyses. We demonstrate ctmmweb’s capabilities, including AKDE home range estimation and subsequent home range overlap analysis, on a dataset of four jaguars from the Brazilian Pantanal. We intend ctmmweb to open AKDE and related autocorrelation-explicit analyses to a wider audience of wildlife and conservation professionals.

Keywords: AKDE; animal movement; autocorrelation; ctmm; telemetry; tracking data

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Permalink: https://www.hzdr.de/publications/Publ-31776
Publ.-Id: 31776


THEREDA – Thermodynamic Reference Database for the nuclear waste disposal in Germany

Bok, F.; Moog, H. C.; Altmaier, M.; Freyer, D.; Thoenen, T.

1 Introduction
The disposal of nuclear waste including the assessment of long-term safety is still an open question in Germany. In addition to the pending decision about the repository host rock (salt, granite, or clay) and the associated site selection, the basic necessity of a consistent and obligatory thermodynamic reference database persists. Such a database is essential to assess potential radionuclide migration scenarios accu-rately and to make well-founded predictions about the long-term safety up to one million years. Specific challenges are comprehensive datasets covering also elevated temperatures and high salinities. Concern-ing the required elements (actinides, fission products as well as matrix and building materials), no other thermodynamic database is available that is compatible with the expected conditions. Due to these defi-ciencies THEREDA [1,2], a joint project of institutions leading in the field of safety research for nuclear waste disposal in Germany and Switzerland, was started in the year 2006.

2 Database features
THEREDA offers evaluated thermodynamic data for many compounds (solid phases, aqueous species, or constituents of the gaseous phase) of elements relevant according to the present state of research. In particular, all oxidation states expected for disposal site conditions are considered. In the present release, THEREDA includes data for actinides and their chemical analogues (Th, U, Np, Pu, Am, Cm & Nd), fission products (Se, Sr, Tc & Cs) and matrix elements (Na, K, Mg, Ca, Al, Si | Cl, SO₄, CO₃). For the calculation of cementitious phases the current version of CEMDATA (18.1) was integrated [3].
THEREDA is based on a relational databank whose structure intrinsically ensures the internal consisten-cy of thermodynamic data. Data considered respond to the needs of both Gibbs Energy Minimizers (ChemApp, GEMS) and Law-of-Mass-Action codes (Geochemist’s Workbench, PHREEQC, ToughReact). The database is designed generically so that it can store interaction parameters for various models. Namely, the PITZER ion interaction approach to describe activity coefficients of hydrated ions and molecules in saline solutions [4] as well as ideal and non-ideal solid solution approaches are consid-ered in the actual dataset.
After free registration, THEREDA is accessible via internet through www.thereda.de. This is not only a portal to view the data itself, their uncertainties and the primary references of the data; it provides also additional information on issues concerning the database. Ready-to-use parameter files are available for download in a variety of formats (geochemical code specific formats and generic ASCII type). They are also used for internal test calculations – one essential element of the quality assurance scheme. The capa-bilities of THEREDA are demonstrated using approx. 400 application case calculations, whose results were compared with experimental values published in literature.

References
[1] Altmaier, M. et al., “THEREDA - Ein Beitrag zur Langzeitsicherheit von Endlagern nuklearer und nichtnuklearer Abfälle”, atw, 53, 249–253 (2008).
[2] Moog, H.C. et al., “Disposal of nuclear waste in host rock formations featuring high-saline solutions – Implementation of a thermodynamic reference database (THEREDA)”, Appl. Geochem., 55, 72–84 (2015).
[3] Lothenbach, B. et al., “Cemdata18: A chemical thermodynamic database for hydrated Portland cements and alkali-activated materials”, Cem. Concr. Res., 115, 472–506 (2019).
[4] Pitzer, K.S., Activity Coefficients in Electrolyte Solutions, 2nd Ed., pp. 542, CRC Press, Boca Raton (1991).
[5] Ryan, J. L., et al. “The solubility of uranium(IV) hydrous oxide in sodium hydroxide solutions under reducing conditions”, Polyhedron, 2, 947 (1983).
[6] Rai, D. et al. “The Solubility of Th(IV) and U(IV) Hydrous Oxides in Concentrated NaCl and MgCl₂ Solutions” Radiochim. Acta, 79, 239–247 (1997).
[7] Neck, V. et al. “Solubility and hydrolysis of tetravalent actinides”, Radiochim. Acta, 89, 1–16 (2001),

Keywords: THEREDA; Thermodynamic database; Nuclear waste disposal; Geochemical modelling; Pitzer ion interaction approach

  • Poster (Online presentation)
    Tage der Standortauswahl, 11.-12.02.2021, Freiberg, Deutschland
  • Lecture (Conference) (Online presentation)
    Tage der Standortauswahl, 11.-12.02.2021, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31775
Publ.-Id: 31775


ctmmweb: A graphical user interface for autocorrelation-informed home range estimation

Calabrese, J.; Fleming, C. H.; Noonan, M. J.; Dong, X.

Estimating animal home ranges is a primary purpose of collecting tracking data. Many widely used home range estimators, including conventional kernel density estimators, assume independently sampled data. In stark contrast, modern GPS animal tracking datasets are almost always strongly autocorrelated. The incongruence between estimator assumptions and empirical reality often leads to systematically underestimated home ranges. Autocorrelated kernel density estimation (AKDE) directly models the observed autocorrelation structure of tracking data during home range estimation, and has been shown to perform accurately across a broad range of tracking datasets. However, compared to conventional estimators, AKDE requires additional modeling steps and has heretofore only been accessible via the command-line ctmm R package. Here, we introduce ctmmweb, which provides a point-and-click graphical interface to ctmm and streamlines AKDE, its prerequisite autocorrelation modeling steps, and a number of additional movement analyses. We demonstrate ctmmweb’s capabilities, including AKDE home range estimation and subsequent home range overlap analysis, on a dataset of four jaguars from the Brazilian Pantanal. We intend ctmmweb to open AKDE and related autocorrelation-explicit analyses to a wider audience of wildlife and conservation professionals.

Keywords: AKDE; animal movement; autocorrelation; ctmm; telemetry; tracking data

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Permalink: https://www.hzdr.de/publications/Publ-31774
Publ.-Id: 31774


Deformation behavior of nanocrystalline body-centered cubic iron with segregated, foreign Interstitial: A molecular dynamics study

Almotasem, A. T.; Posselt, M.; Polcar, T.

In the present work, modified embedded atom potential and large-scale molecular dynamics’ simulations were used to explore the effect of grain boundary (GB) segregated foreign interstitials on the deformation behavior of nanocrystalline (nc) iron. As a case study, carbon and nitrogen (about 2.5 at.%) were added to (nc) iron. The tensile test results showed that, at the onset of plasticity, grain boundary sliding mediated was dominated, whereas both dislocations and twinning were prevailing deformation mechanisms at high strain. Adding C/N into GBs reduces the free excess volume and consequently increases resistance to GB sliding. In agreement with experiments, the flow stress increased due to the presence of carbon or nitrogen and carbon had the stronger impact. Additionally, the simulation results revealed that GB reduction and suppressing GBs’ dislocation were the primary cause for GB strengthening. Moreover, we also found that the stress required for both intragranular dislocation and twinning nucleation were strongly dependent on the solute type.

Keywords: iron; molecular dynamics; segregation; dislocation; twinning

Permalink: https://www.hzdr.de/publications/Publ-31773
Publ.-Id: 31773


Investigations of internal stresses in high-voltage devices with deep trenches

Hieckmann, E.; Mühle, U.; Chekhonin, P.; Zschech, E.; Gambino, J.

Deep trenches, as essential elements of silicon chips used in electronic high-power and high-frequency devices, are known as starting points for dislocation generation under the influence of internal mechanical stresses resulting mainly from the difference in the thermal expansion coefficients between silicon and silicon dioxide. Since the electrical insulation of the devices requires a sequence of mechanical, chemical, and high-temperature processes during the preparation of the deep trenches, including the formation of an amorphous SiO2 edge layer, the emergence of the internal stresses is hardly avoidable. The method of cross correlation backscattered electron diffraction in the scanning electron microscope is used here to quantitatively determine the magnitude and local distribution of internal stresses in silicon around the deep trenches after four different process steps. For this purpose, Kikuchi diffraction images are recorded of the wafer cross section areas along lines perpendicular and parallel to the deep trenches. After Fourier transformation, these images are cross correlated with the Fourier transform of the diffraction image from a stressfree reference sample site. The well-established numerical evaluation of cross correlation functions provides the complete distortion tensor for each measuring point of the line scan, from which the stress tensor can be calculated using Hooke’s law. It is found that the in-plane normal stress component σ11 perpendicular to the long edges of the deep trench is larger than the other stress components. That means it essentially determines the magnitude of the von-Mises stress, which was determined as a general stress indicator for all measuring points, too. A characteristic feature is the local distribution of the stress component σ11 with maximum tensile stresses of some hundred megapascals at transition between Si and amorphous SiO2 on the long edges of the deep trench, and with even higher maximum compressive stresses immediately below the bottom of the deep trench. At a distance of about 2 μm from the edges of a single deep trench, all stress components decrease to negligibly small values so that steep stress gradients occur. The range and distribution of tensile and compressive stresses are in accordance with finite element simulations; however, the measured stresses are higher than expected for all investigated states so that dislocation formation seems to be possible. The influence of the electron acceleration voltage on the determination of the internal stresses is discussed as well.

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Permalink: https://www.hzdr.de/publications/Publ-31772
Publ.-Id: 31772


Data for: Electron-phonon coupling in n-type Ge two-dimensional systems

Ciano, C.; Persichetti, L.; Montanari, M.; Di Gaspare, L.; Capellini, G.; Baldassarre, L.; Ortolani, M.; Pashkin, O.; Helm, M.; Winnerl, S.; Virgilio, M.; de Seta, M.

Summary of degenerate pump-probe experiment on SiGe QWs for nonradiative lifetime estimation
 FELBE beamtime 04-07 April 2019

  • : alignment and measure of a rectangular structure (2261) featuring intersubband transition above the longitudinal - optical phonon. FEL wavelength 26.5 mm.
  • : measure of a rectangular structure (2263) featuring intersubband transition below the longitudinal - optical phonon and of an asymmetric-coupled QWs structure (2217). FEL wavelength 45.8 mm.
  • : measure of the same rectangular structure (2263) and of a step well (2264). FEL wavelength 52.6 mm.
  • : measure of the same rectangular structure (2263), of the step well (2264) and of another ACQW (2216) at much lower pump intensities. FEL wavelength 45.8 mm and 52.6 mm.

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Permalink: https://www.hzdr.de/publications/Publ-31771
Publ.-Id: 31771


CdTe refining + photovoltaic manufacturing + recycling HSC model

Heibeck, M.; Bartie, N. J.; Abadias Llamas, A.; Reuter, M.
Project Leader: Heibeck, Magdalena; Supervisor: Bartie, Neill Jacques; Supervisor: Abadias Llamas, Alejandro; Supervisor: Reuter, Markus Andreas

This file contains an HSC model for cadmium and tellurium refining starting from by-products coming from a copper precious metals refinery, lead and zinc flowsheets, manufacturing of a CdTe photovoltaic module and its recycling process based on data found in literature. The model was used to perform a resource efficiency, including exergy, and environmental impact (LCA) evaluation of the life cycle of a CdTe photovoltaic module. This model was used in the Master’s thesis “Simulation-based assessment of resource efficiency and environmental impacts of a CdTe photovoltaic life cycle” by Magdalena Heibeck and for the publications “The simulation-based analysis of the circular economy – the enabling role of metallurgical infrastructure” published in the “Mineral Processing and Extractive Metallurgy” journal on 08/11/2019 (https://doi.org/10.1080/25726641.2019.1685243) and “Simulation-based Exergy Analysis of Large Circular Economy Systems: Zinc Production Coupled to CdTe Photovoltaic Module Life Cycle” published in the “Journal of Sustainable Metallurgy” on 17/12/2019 (https://doi.org/10.1007/s40831-019-00255-5).

Detailed information about the literature sources used for developing the model can be found in the references above.

The model can only be opened with HSC software and was made with HSC version 10.0.0.5 (https://www.outotec.com/HSC).

Keywords: Process Simulation Model; Resource Efficiency; Photovoltaics; Recycling; LCA; Exergy; Digital Twin; Metallurgy

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Permalink: https://www.hzdr.de/publications/Publ-31770
Publ.-Id: 31770


Validation of Serpent-SCF-TU full-core pin-by-pin burnup calculations using Pre-Konvoi PWR experimental data

Garcia, M.; Bilodid, Y.; Basualdo Perello, J.; Tuominen, R.; Gommlich, A.; Leppanen, J.; Valtavirta, V.; Imke, U.; Ferraro, D.; van Uffelen, P.; Seidl, M.; Sanchez-Espinoza, V.

The focus of this work is the validation of Serpent-SCF-TU, a high-fidelity multiphysics tool combining Monte Carlo neutron transport, subchannel thermalhydraulics and fuel-performance analysis. A full-core pin-by-pin depletion calculation for the first operating cycle of a Pre-Konvoi PWR plant is presented and the results are assessed using experimental data. The critical boron concentration and a set of pin-level neutron flux profiles are compared against measurements, with very good agreement. The impact of using fuel performance analysis is discussed as well, comparing the three-code coupling with the traditional neutronic-thermalhydraulic approach. The studies presented here are part of the final stage of the EU Horizon 2020 McSAFE project, closing the development cycle of the Serpent-SCF-TU system, from implementation to validation.

Keywords: Serpent-SCF-TU; Monte Carlo transport; High-fidelity multiphysics; Pin-level burnup; Pre-Konvoi PWR

Permalink: https://www.hzdr.de/publications/Publ-31768
Publ.-Id: 31768


Development of the First Potential Nonpeptidic Positron Emission Tomography Tracer for the Imaging of CCR2 Receptors

Wagner, S.; De, M. G. F.; Silva, D.; Ortiz, Z. N.; Zweemer, A.; Hermann, S.; De, M. M.; Koch, M.; Weiss, C.; Schepmann, D.; Heitman, L.; Tschammer, N.; Kopka, K.; Junker, A.

Herein we report the design and synthesis of a series of highly selective CCR2 antagonists as 18F-labeled PET tracers. The derivatives were evaluated extensively for their off-target profile at 48 different targets. The most potent and selective candidate was applied in vivo in a biodistribution study, demonstrating a promising profile for further preclinical development. This compound represents the first potential nonpeptidic PET tracer for the imaging of CCR2 receptors.

Keywords: CCR2; CCR5 antagonists; chemokine receptors; molecular imaging; PET; radiolabeling; TAK-779

Permalink: https://www.hzdr.de/publications/Publ-31767
Publ.-Id: 31767


Unconventional Hall response in the quantum Limit of HfTe5

Galeski, S.; Zhao, X.; Wawrzynczak, R.; Meng, T.; Förster, T.; Lozano, P. M.; Honnali, S.; Lamba, N.; Ehmcke, T.; Markou, A.; Li, Q.; Gu, G.; Zhu, W.; Wosnitza, J.; Felser, C.; Chen, G. F.; Gooth, J.

Interacting electrons confined to their lowest Landau level in a high magnetic field can form a variety of correlated states, some of which manifest themselves in a Hall effect. Although such states have been predicted to occur in three-dimensional semimetals, a corresponding Hall response has not yet been experimentally observed. Here, we report the observation of an unconventional Hall response in the quantum limit of the bulk semimetal HfTe5, adjacent to the three-dimensional quantum Hall effect of a single electron band at low magnetic fields. The additional plateau-like feature in the Hall conductivity of the lowest Landau level is accompanied by a Shubnikov-de Haas minimum in the longitudinal electrical resistivity and its magnitude relates as 3/5 to the height of the last plateau of the three-dimensional quantum Hall effect. Our findings are consistent with strong electron-electron interactions, stabilizing an unconventional variant of the Hall effect in a three-dimensional material in the quantum limit.

Permalink: https://www.hzdr.de/publications/Publ-31765
Publ.-Id: 31765


Beam modeling of a proton pencil beam scanning beam line integrated with a low-field open MR scanner

Sepúlveda, C.; Gebauer, B.; Hoffmann, A. L.; Lühr, A.; Oborn, B.; Burigo, L.

Objective: The integration of an MRI scanner into a proton beam line imposes challenges to the dose delivery, since the magnetic field (MF) of the scanner distorts the beams and hence the dose distribution. This study aims to develop a Monte Carlo (MC)-based beam model of the pencil beam scanning nozzle in the OncoRay facility to accurately model the dose delivery in the presence of an open MR scanner.
Materials and Methods: Measurements of proton beam spot size in air at varying distance from the nozzle were used to model beam optics using the Geant4-based MC code TOPAS. The beam energy and energy spread were obtained from the fit of depth-dose profiles measured in water.
A 3D map of the magnetic fringe field of the 0.22 T (vertical field) open MR scanner was generated with COMSOL and used in TOPAS. The simulated beam deflection was compared to measurements 210 cm downstream of the beam isocenter. Horizontal spot scanning positions from 0 to 200 mm and beam energies of 125 and 220 MeV were considered.
Results: The simulated spot sizes without MF agreed with experimental measurements within the experimental uncertainty. With MF, spot deflections of 183.6 (125 MeV) and 135.0 (220 MeV) mm were observed at the central spot position in the horizontal axis compared to their respective experimental values of 226.5 and 164.6 mm. For scan positions from 50 to 200 mm, relative differences between simulations and experimental results were within 6% (125 MeV) and 3.7% (220 MeV).
Conclusions: In the absence of MF, Initial validation of the beam modeling shows good reproducibility of spot sizes. Simulations with MF show large deviations for the beam deflection for central beam spots. The observed disagreement is likely related to deficiencies in the MF map, which has not been experimentally validated. Future work will include the validation of the MF map and a detailed evaluation of beam deflection and changes in spot sizes in the MF.

Keywords: Monte Carlo Simulation; MRiPT

  • Lecture (Conference) (Online presentation)
    8th MRinRT 2021, 19.-21.04.2021, Heidelberg (online), Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31764
Publ.-Id: 31764


Reduced white matter diffusion in glioblastoma patients after radiotherapy with photons and protons

Dünger, L.; Raschke, F.; Seidlitz, A.; Jentsch, C.; Platzek, I.; Kotzerke, J.; Beuthien-Baumann, B.; Baumann, M.; Krause, M.; Troost, E. G. C.

Introduction:

Radio(chemo)therapy is standard in the (adjuvant) treatment of glioblastoma. Inevitably, brain tissue surrounding the tumor bed or residual tumor is also irradiated, which may lead to acute and late side-effects. Diffusion-weighted imaging (DWI) with magnetic resonance imaging (MRI) has been shown to be a sensitive method to detect early changes in the cerebral white matter after radiation. The aim of this work was to assess possible changes in the mean diffusivity (MD) of the white matter after radio(chemo)therapy using DWI and to compare these effects between patients treated with proton and photon irradiation.
Patients & methods:
70 patients diagnosed with glioblastoma underwent adjuvant radio(chemo)therapy with protons (n=20) or photons (n=50). MRI follow-up examinations were performed at three-monthly intervals and were evaluated until 33 months after the end of therapy. For all time points, MD maps were calculated and normal appearing white matter was segmented in T1-weighted MR images. Relative white matter MD changes between baseline and all follow-up visits were calculated in different dose regions.
Results:
We observed a significant decrease of MD (mean -4,0%, range -0,8 ¬– -7,9%, p<0.05) in white matter in areas, in which a dose of more than 20 Gy had been applied. The MD reduction was progressing with dose and time after radio(chemo)therapy. In patients treated with photons, significant reductions in white matter in the whole brain (mean -2,3%, range -0,9 – -3,1%, p<0.05) were seen at all time points. In proton patients, conversely, MD did not change significantly (mean -0,5%, range 0,5 – -2,4%).
Conclusion:
The results show that irradiation leads to measurable changes in white matter and that treatment with protons reduces this effect due to a lower total dose in the surrounding white matter. Further investigations are needed to assess whether those MD changes correlate with known radiation induced side-effects.

  • Lecture (Conference)
    MRinRT 2021, 19.-21.04.2021, Heidelberg, BRD

Permalink: https://www.hzdr.de/publications/Publ-31763
Publ.-Id: 31763


Screening Arrays of Laminin Peptides on Modified Cellulose for Promotion of Adhesion of Primary Endothelial and Neural Precursor Cells

Wetzel, R.; Hauser, S.; Lin, W.; Berg, P.; Werner, C.; Pietzsch, J.; Kempermann, G.; Zhang, Y.

Neural precursor cells (NPC) are primary cells intensively used in the context of research on adult neurogenesis and modelling of neuronal development in health and diseased states. Substrates that can facilitate NPC adhesion will be very useful for culturing these cells. Due to the presence of laminin in basal lamina as well as their involvement in differentiation, migration, and adhesion of many types of cells, we focused on surfaces modified with laminin-derived peptides and compared them with the widely used fibronectin-derived RGD peptides. We synthesized an array of 46 peptides on cellulose paper (SPOT) to identify laminin-derived peptides that promote short-term adhesion of murine NPC and human primary endothelial cells. Various previously reported peptide sequences have been re-evaluated in this work. Initial adhesion experiments showed NPC preferred several laminin-derived peptides by up to 5-time higher cell numbers, compared to the well-known promiscuous integrin binding RGD peptide. Importantly, screening of cell adhesion has revealed a synergetic effect of filamentous matrix, peptide sequence, surface property, ligand density, and the dynamic process of NPC adhesion.

Keywords: peptide array; SPOT synthesis; laminin peptides; neural precursor cells; endothelial cells

Permalink: https://www.hzdr.de/publications/Publ-31762
Publ.-Id: 31762


Coordination of Trivalent Lanthanum and Cerium, and Tetravalent Cerium and Actinides (An = Th(IV), U(IV), Np(IV)) by a 4-Phosphoryl 1H-Pyrazol-5-olate Ligand in Solution and the Solid State

Zhang, J.; Wenzel, M.; Schnaars, K.; Hennersdorf, F.; Schwedtmann, K.; März, J.; Roßberg, A.; Kaden, P.; Kraus, F.; Stumpf, T.; Weigand, J. J.

Structural investigations of three actinide(IV) 4-phosphoryl 1H-pyrazol-5-olate complexes (An = Th(IV), U(IV), Np(IV)) and their cerium(IV) analogue display the same metal coordination in the solid state. The mononuclear complexes show the metal centre in a square antiprismatic coordination geometry composed by the two O-donor atoms of four deprotonated ligands. Detailed solid state analysis of the U(IV) complex shows that in dependence of the solvent used altered arrangements are observable, resulting in a change in the coordination polyhedron of the U(IV) metal centre to bi-capped trigonal prismatic. Further, single crystal analyses of the La(III) and Ce(III) complexes show that the ligand can also act as a neutral ligand by protonation of the pyrazoyl moiety. All complexes were comprehensively characterized by NMR, IR and Raman spectroscopy. A single resonance in each of the 31P NMR spectra for the La(III), Ce(III), Ce(IV), Th(IV) and Np(IV) complex indicates the formation of highly symmetric complex species in solution. Extended X-ray absorption fine structure (EXAFS) investigations provide evidence for the same local structure of the U(IV) and Np(IV) complex in toluene solution, confirming the observations made in the solid state.

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Permalink: https://www.hzdr.de/publications/Publ-31761
Publ.-Id: 31761


Comparative Studies of Light-Responsive Swimmers: Janus Nanorods versus Spherical Particles

Eichler-Volf, A.; Huang, T.; Vazquez Luna, F.; Alsaadawi, Y.; Stierle, S.; Cuniberti, G.; Steinhart, M.; Baraban, L.; Erbe, A.

The shape of objects has a strong influence on their dynamics. Here, we present comparative studies of two different motile objects, spherical Ag/AgCl Janus particles and polystyrene Janus nanorods, that move due to an ionic self-diffusiophoretic propulsion mechanism when exposed to blue light. In this paper, we propose a method to fabricate Janus rodlike particles with high aspect ratios and hemispherical tip shapes. The inherent asymmetry due to the ratio between capped and uncapped parts of the particles as well as the shape anistropy of Janus nanorods enables imaging and quantification of rotational dynamics. The dynamics of microswimmers are compared in terms of velocities and diffusion coefficients. We observe that despite a small amount of the Ag/AgCl reagent on the surface of rodlike objects, these new Janus micromotors reveal high motility in pure water. While the velocities of spherical particles reach 4.2 μm/s, the single rodlike swimmers reach 1.1 μm/s, and clusters reach 1.6 μm/s. The effect of suppressed rotational diffusion is discussed as one of the reasons for the increased velocities. These Janus micro- and nanomotors hold the promise for application in light-controlled propulsion transport.

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Permalink: https://www.hzdr.de/publications/Publ-31760
Publ.-Id: 31760


Nano-hillock formation on CaF2 due to individual slow Au-cluster impacts

Szabo, G. L.; Lehner, M.; Bischoff, L.; Pilz, W.; Kentsch, U.; Aumayr, F.; Klingner, N.; Wilhelm, R. A.

Ion-irradiation and the induced nanostructuring was found, over the last century, to be a very powerful technique for surface modifications on a vast amount of different materials. Especially the formation of nanostructures by strong electronic excitation mediated by slow highly charged ions and swift heavy ions received lots of interest in recent years. The ionic crystal CaF2 was a model system for the underlying processes. In our investigations we reveal the formation of nano-hillocks by slow individual Au-cluster-irradiation on CaF2(111) surface that were found to be very similar to nano-hillocks in former studies with highly charged ions. We show that the high energy density directly transferred to the atomic lattice of the target leads to the same hillock-like structures as in case of indirect energy transfer for slow highly charged ions.

Keywords: Cluster-irradiation; nanostructure formation; nano-hillocks; LMAIS; CaF2

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Permalink: https://www.hzdr.de/publications/Publ-31759
Publ.-Id: 31759


TOPFLOW Pressure Chamber – versatile techniques to simplify design and instrumentation of thermal fluid dynamic experiments at high pressure

Prasser, H.-M.; Hampel, U.; Schütz, P.

The present paper describes the design and function of the TOPFLOW Pressure Chamber of the Helmholtz Zentrum Dresden-Rossendorf. The facility opened new opportunities for experiments at pressures of up to 50 bar. The actual test equipment can be constructed as a not pressure carrying installation. The TOPFLOW steam generator, located in an adjacent hall, was used to supply steam at saturation conditions. In the paper, three experimental programs that were carried out in the pressure chamber are introduced briefly, mainly with the purpose to highlight the advantages of the pressure chamber technique.

Keywords: TOPFLOW; Pressure chamber; Experimental program; Infrared observation; Video recording of the flow structure

Permalink: https://www.hzdr.de/publications/Publ-31758
Publ.-Id: 31758


Determination of magnetic field correction factors for dosimetry in MR-integrated proton therapy

Gebauer, B.; Sepulveda, C.; Burigo, L.; Pawelke, J.; Hoffmann, A. L.; Lühr, A.

Objectives: For the integration of magnetic resonance imaging (MRI) into proton therapy (PT), a 0.22 T MRI was installed at the pencil beam scanning beam line at OncoRay. As a next step, dosimetry in the magnetic field has to be established. This work aims to study the influence of the static field (B0) of the MRI on ionisation chamber (IC) responses for proton beams through measurements and Monte Carlo (MC) simulations.
Materials & methods: A Semiflex 0.3 and a PinPoint 3D IC were positioned in a water phantom placed in the MR imager isocenter. The absolute dose at five proton energies (70, 110, 150, 190, 226.7 MeV) was measured within the entrance plateau of the depth-dose curve using a 10×10 cm² homogeneous irradiation field. The correction factor kB→,M,Q was obtained by dividing the measured dose with/without B0. For the MC simulations, beam-commissioning data (depth-dose profiles in water, beam spot sizes in air) were used to create a MC beam model in TOPAS (1.5×105 particles). A 3D map of the scanner’s magnetic field (MF) was calculated with COMSOL and used in the simulations to mimic the experimental setup.
Results: The MF correction factor kB→,M,Q showed systematic energy-dependent differences between dose readings with and without B0. For the Semiflex 0.3, kB→,M,Q was 0.9926, 0.9942, 0.9941, 0.9959 and 1.0036 for 70, 110, 150, 190 and 226.7 MeV, respectively. For the same energies, kB→,M,Q for the PinPoint 3D was 0.9920, 0.9931, 0.9938, 0.9952 and 0.9969. For all energies, the standard deviations of kB→,M,Q were smaller than 0.002 for both ICs. MC simulations of the Semiflex 0.3 response to 110 MeV showed no statistically significant B0 effect with kB→,M,Q of 0.997 (95% CI: 0.9893, 1.0049).
Conclusion: Measurements showed a small but significant influence of the MRI scanner’s B0 field on the IC response, which was beam energy-dependent. Further investigations should clarify the necessity of dosimetric correction factors for the MR-integrated PT.

Keywords: MRiPT; Monte Carlo Simulation; dosimetry; proton therapy; MRI

  • Lecture (Conference) (Online presentation)
    8th MRinRT 2021, 19.-21.04.2021, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31757
Publ.-Id: 31757


Insights into the Electronic Structure of a U(IV) Amido and U(V) Imido Complex

Köhler, L.; Patzschke, M.; Bauters, S.; Vitova, T.; Butorin, S. M.; Kvashnina, K.; Schmidt, M.; März, J.; Stumpf, T.

Reaction of the N-heterocylic carbene ligand iPrIm (L1) and lithium bis(trimethylsilyl)amide (TMSA) as a base with UCl4 resulted in U(IV) and U(V) complexes. Uranium’s +V oxidation state in (HL1)2[U(V)(TMSI)Cl5] (TMSI = trimethylsilylimido) (2) was confirmed by HERFD-XANES measurements. Solid state characterization by SC-XRD and geometry optimisation of [U(IV)(L1)2(TMSA)Cl3] (1) indicated a silylamido ligand mediated inverse trans influence (ITI). The ITI was examined regarding different metal oxidation states and was compared to transition metal analogues by theoretical calculations.

Keywords: Uranium (V); carbenes; HERFD XANES; inverse trans influence

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Permalink: https://www.hzdr.de/publications/Publ-31756
Publ.-Id: 31756


On the consensus nomenclature rules for radiopharmaceutical chemistry – reconsideration of radiochemical conversion

Herth, M.; Ametamey, S.; Antuganov, D.; Bauman, A.; Berndt, M.; Brooks, A.; Bormans, G.; Choe, Y.; Gillings, N.; Häfeli, U.; James, M.; Kopka, K.; Kramer, V.; Krasikova, R.; Madsen, J.; Mu, L.; Neumaier, B.; Piel, M.; Rösch, F.; Ross, T.; Schibli, R.; Scott, P.; Shalgunov, V.; Vasdev, N.; Wadsak, W.; Zeglis, B.

Radiochemical conversion is an important term to be included in the “Consensus nomenclature rules for radiopharmaceutical chemistry”. Radiochemical conversion should be used to define reaction efficiency by measuring the transformation of components in a crude reactionmixture at a given time,whereas radiochemical yield is better suited to define the efficiency of an entire reaction process including, for example, separation, isolation, filtration, and formulation.

Keywords: Nomenclature; Terminology; Consensus guidelines; Radiopharmaceutical sciences; Nuclear chemistry; Radiochemistry; Radiochemical conversion; Radiochemical yield

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Permalink: https://www.hzdr.de/publications/Publ-31755
Publ.-Id: 31755


Simulation of bubble dynamics under pool scrubbing conditions

Liao, Y.; Lucas, D.

Pool scrubbing is an effective method for removing radioactive aerosols during severe nuclear accidents and protecting the health of nearby residents and the environment. After the pool scrubbing research is revived by the Fukushima Daiichi accident, experimental studies tend to provide CFD-level data on phase distribution and bubble dynamics owing to improved measuring techniques. In contrast, CFD investigations on bubble dynamics under pool scrubbing conditions are still scarce due to the challenges of reliable models and high computational cost. To achieve best practice guidelines for the use of CFD for such complex multiphase flow situations in nuclear safety analyses, there is still a long way to go and a large amount of simulation practice is desirable. This work aims to investigate the bubble dynamics under pool scrubbing conditions using the interface-tracking method available in the open-source CFD code OpenFOAM. At first, the impact of numerical setups such as domain dimension, mesh resolution, and time step on the simulation results is studied in detail for a basic case, which provides good guidelines for the setup of next benchmark cases. Bubble shape, bubble detachment size, and frequency as well plume structure are compared with the results of other institutions that participate in the benchmark simulations as well as experimental observations. Good qualitative and quantitative agreement was obtained. The work provides a basis for investigation on bubble dynamics in pool scrubbing with aerosol particles using the CFD methodology in the next step.

Keywords: Bubble dynamics; Pool scrubbing; CFD; Nuclear reactor safety; OpenFOAM

  • Contribution to proceedings
    V-CFD4NRS8, 25.-27.11.2020, virtual, France
  • Lecture (Conference) (Online presentation)
    V-CFD4NRS8, 25.-27.11.2020, Virtual, France

Permalink: https://www.hzdr.de/publications/Publ-31753
Publ.-Id: 31753


Barium-131 as starting point for the development of radiotheranostic approaches

Reissig, F.; Bauer, D.; Ullrich, M.; Kreller, M.; Kopka, K.; Pietzsch, J.; Pietzsch, H.-J.; Walther, M.; Mamat, C.

We understand 131Ba as a radionuclide, which enables imaging by SPECT in nuclear medicine and provides a diagnostic match for the therapeutic alpha-emitting radionuclides 223Ra and 224Ra. Recently, we reported on a sufficient production route for 131Ba by irradiating a 133Cs target with 27.5 MeV proton beams, and the straight-forward resin-based radiochemical separation, yielding 131Ba with high radionuclide purity. An average amount of 190 MBq of 131Ba was produced per irradiation. Apart from 0.1% isotopic impurity of 133Ba, no more side-products were detectable. For the first time, radiolabeling of the complexing agent macropa (known to be an appropriate 225Ac chelator) with 131Ba was reported and mild labeling conditions as well as reaction control using TLC systems were applicable. The radiopharmacological characterization of 131Ba-labeled macropa was carried out in healthy mice using uncomplexed [131Ba]Ba2+ as a reference, including biodistribution studies and small animal SPECT/CT. The results revealed the rapid bone uptake of free [131Ba]Ba2+ ions, whereas 131Ba-labeled macropa showed a fast renal clearance and significantly lower (P < 0.001) accumulation in the bones. We therefore conclude, that 131Ba is a promising “new” radionuclide for SPECT imaging purposes and delivers appropriate quality for preclinical investigations. Moreover, the successful labeling of macropa and the in vivo stability of the 131Ba-complex are viewed as a promising starting point for the development of new heavy earth alkaline metal chelators, especially for the therapeutically relevant radium isotopes. This enables 131Ba to achieve its goal as diagnostic match and monitoring tool for 223/224Ra.

Keywords: Barium-131; SPECT; Radium-223; Theranostics; Radium-224

  • Open Access Logo Lecture (Conference) (Online presentation)
    6th International Electronic Conference on Medicinal Chemistry (ECMC2020), 01.-30.11.2020, Basel, Schweiz
    DOI: 10.3390/ECMC2020-07459

Permalink: https://www.hzdr.de/publications/Publ-31752
Publ.-Id: 31752


Electron-phonon coupling in n-type Ge two-dimensional systems

Ciano, C.; Persichetti, L.; Montanari, M.; Di Gaspare, L.; Capellini, G.; Baldassarre, L.; Ortolani, M.; Pashkin, O.; Helm, M.; Winnerl, S.; Virgilio, M.; de Seta, M.

Electron-optical phonon interaction is the dominant energy-loss mechanism in low-dimensional Ge/SiGe heterostructures and represents a key parameter for the design and realization of electronic and optoelectronic devices based on this material system compatible with the mainstream Si complementary metal-oxide semiconductor technology. Here we investigate the intersubband relaxation dynamics of n-type Ge/SiGe multiquantum wells with different symmetry and design by means of single-color pump-probe spectroscopy. By comparing the experimental differential transmittance data as a function of the pump-probe delay with numerical calculations based on an energy-balance rate-equation model, we could quantify an effective value for the optical phonon deformation potential describing the electron-phonon coupling in two-dimensional Ge-based systems. We found nonradiative relaxation times longer than 20 ps even in samples having intersubband energy separations larger than the optical phonon energy, evidencing the presence of a less effective electron-phonon coupling with respect to that estimated in bulk Ge.

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Permalink: https://www.hzdr.de/publications/Publ-31751
Publ.-Id: 31751


KRAS mutation effects on the 2-[18F]FDG PET uptake of colorectal adenocarcinoma metastases in the liver

Popovic, M.; Talarico, O.; van den Hoff, J.; Kunin, H.; Zhang, Z.; Lafontaine, D.; Dogan, S.; Leung, J.; Kaye, E.; Czmielewski, C.; Et Al, S.

Background:

Deriving individual tumor genomic characteristics from patient imaging analysis is desirable. We explore the predictive value of 2-[18F]FDG uptake with regards to the KRAS mutational status of colorectal adenocarcinoma liver metastases (CLM).
Methods:
2-[18F]FDG PET/CT images, surgical pathology and molecular diagnostic reports of
37 patients who underwent PET/CT-guided biopsy of CLM were reviewed under an IRB-approved retrospective research protocol. Sixty CLM in 39 interventional PET scans of the 37 patients were segmented using two different auto-segmentation tools implemented in 37 different commercially available software packages. PET standard uptake values (SUV) were corrected for: 1) partial volume effect (PVE) using cold wall-corrected contrast recovery coefficients derived from phantom spheres with variable diameter; and 2) variability of arterial tracer supply and variability of uptake time after injection until start of PET scan derived from the tumor-to-blood standard uptake ratio (SUR) approach. The correlations between the KRAS mutational status and the mean, peak, and maximum SUV were investigated using Student’s t-test, Wilcoxon rank sum test with continuity correction, logistic regression and receiver operation characteristic (ROC) analysis. These correlation analyses were also performed for the ratios of the mean, peak and maximum tumor uptake to the mean blood activity concentration at the time of scan: SURMEAN, SURPEAK, and SURMAX, respectively.
Results: Fifteen patients harbored KRAS missense mutations (KRAS+) while another 3 harbored KRAS gene amplification. For 31 lesions the mutational status was derived from the PET/CT-guided biopsy. The Student’s-t p-values for separating KRAS mutant cases decreased after applying PVE correction to all uptake metrics of each lesion and when applying correction for uptake time variability to the SUR metrics. The observed correlations were strongest when both corrections were applied to SURMAX and when the patients harboring gene amplification were grouped with the wild type: p ≤ 0.001; ROC area under the curve (AUC) = 0.77 and 0.75 for the two different segmentations respectively with a mean specificity of 0.69 and sensitivity of 0.85.
Conclusions:
The correlations observed after applying the described corrections show potential for assigning probabilities for the KRAS missense mutation status in CLM using 2-[18F]FDG PET images.

Keywords: PET; colorectal adenocarcinoma; liver metastases; KRAS mutations

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Permalink: https://www.hzdr.de/publications/Publ-31750
Publ.-Id: 31750


Solid-liquid flow in Stirred Tanks: Euler-Euler / RANS Modeling

Rzehak, R.; Shi, P.

Stirred tanks are widely used equipment to process solid-liquid dispersions in the chemical and minerals engineering industries. CFD simulations of such equipment on industrial scales are principally feasible within the Euler-Euler / RANS approach. Practical application, however, requires suitable closure models to account for phenomena on the scale of individual particles, which are not resolved in this approach. The present work applies a set of closure relations that originates from a comprehensive review of existing results from analytical, numerical, and experimental studies. Focus is on the modeling of interfacial forces which includes drag, lift, and turbulent dispersion. To validate the model a comprehensive set of experimental data including particle concentration as well as liquid velocity and turbulence has been assembled from different literature sources. The necessity for model extensions is confirmed via the comparison of simulation results obtained by different sets of closure correlations, i.e. the presently proposed one and others that have been frequently used in previous studies, with the experimental data.

Keywords: multiphase CFD simulation; particulate flow; closure modeling; stirred tanks

  • Lecture (Conference)
    14th International Conference on Computational Fluid Dynamics In the Oil & Gas, Metallurgical and Process Industries (CFD2020), 12.-14.10.2020, Trondheim, Norway

Permalink: https://www.hzdr.de/publications/Publ-31749
Publ.-Id: 31749


Euler-Euler modeling of reactive flows in bubble columns

Rzehak, R.

In the present project, closure models for chemical reactions as well as the as-sociated mass transport are included in the Euler-Euler description of bubbly flows. This approach allows to capture inhomogeneous distributions of gas fraction as well as local differences in concentration and flow fields on the scale of the bubble column. In this way, calculations up to the size of industrial equipment or components thereof become feasible. To achieve this goal, suit-able closure models for processes occurring on the scale of individual bubbles have to be devised. The simulation results, are then compared with experi-mental data to validate the employed models.
The challenge in this endeavor based on the state-of-the-art at the beginning of the project is threefold: First, the available understanding of mass transfer from or to single bubbles both without and with the simultaneous occurrence of a chemical reaction is limited. Second, experimental data of a quality, which is suitable for the purpose of model validation, are scarce. Third, for re-active systems the intrinsic reaction kinetics and material parameters depend-ing on the concentrations of all involved species and temperature are often not known.

Keywords: multiphase CFD simulation; mass transfer; chemical reaction; closure modeling; bubble columns

Permalink: https://www.hzdr.de/publications/Publ-31748
Publ.-Id: 31748


Direct tray and point efficiency measurements including weeping effects through a convenient addon for air/water simulators

Marchini, S.; Vishwakarma, V.; Schubert, M.; Brunazzi, E.; Hampel, U.

A direct approach for determining the tray and point efficiencies of an industrial-scale distillation tray is proposed. The stripping of isobutyl acetate from an aqueous solution with air was used, which is a manageable and non-hazardous method applicable for performance tests in large hydraulic column mockups. This work represents the first application of this system in the case of tray columns exemplified for a sieve tray. A column of 800 mm internal diameter was used for conducting the stripping experiments. The distribution of isobutyl acetate in the liquid phase on the tray was obtained via liquid sampling at several deck positions and UV-spectroscopy analysis. A definition for the liquid-side tray efficiency at weeping conditions is proposed together with an experimental approach for determining tray and point efficiencies in such conditions. The derived efficiency data show a good agreement with the model predictions and correlations.

Keywords: tray efficiency; point efficiency; isobutyl acetate stripping; tray column; mockup revamp; weeping

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Permalink: https://www.hzdr.de/publications/Publ-31747
Publ.-Id: 31747


Benchmarking of computational fluid dynamic models for bubbly flows

Colombo, M.; Rzehak, R.; Fairweather, M.; Liao, Y.; Lucas, D.

Eulerian-Eulerian computational fluid dynamic (CFD) models allow the prediction of complex and large-scale industrial multiphase gas-liquid bubbly flows with a relatively limited computational load. However, the interfacial transfer processes are entirely modelled, with closure relations that often dictate the accuracy of the entire model. Numerous sets of closures have been developed, often optimized over few experimental data sets and achieving remarkable accuracy that, however, becomes difficult to replicate outside of the range of the selected data. This makes a reliable comparison of available model capabilities difficult and obstructs their further development. In this paper, the CFD models developed at the University of Leeds and the Helmholtz-Zentrum Dresden-Rossendorf are benchmarked against a large database of bubbly flows in vertical pipes. The research groups adopt a similar modelling strategy, aimed at identifying a single universal set of widely applicable closures. The main focus of the paper is interfacial momentum transfer, which essentially governs the void fraction distribution in the flow, and turbulence modelling closures. To focus on these aspects, the validation database is limited to experiments with a monodispersed bubble diameter distribution. Overall, the models prove to be reliable and robust and can be applied with confidence over the range of parameters tested. Areas are identified where further development is needed, such as the modelling of bubble-induced turbulence and the near-wall region. A benchmark is also established and is available for the testing of other models. Similar exercises are encouraged to support the confident application of multiphase CFD models, together with the definition of a set of experiments accepted community-wide for model benchmarking.

Keywords: computational fluid dynamics; multiphase flows; bubbly flows; interfacial closures; multiphase turbulence

Permalink: https://www.hzdr.de/publications/Publ-31746
Publ.-Id: 31746


Multiconfigurational calculations of ground state and excited states of tetravalent uranium complexes

Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.

The peculiarities of computational actinide chemistry concerning the ground and excited state require state-of-the-art electronic structure methods. Currently, the most popular one is the CASSCF- method for the inclusion of static correlation in combination with CASPT2 for dynamic correlation and CASSI for spin-orbit coupling. This combination is used for the evaluation of excited state energies and transitions for simulating electronic spectra and comparing with experimental findings. Furthermore, for the evaluation of a proper active space the DMRG method is used for a choice based on objective reasonings. It is found, that the CASSCF+CASPT2+CASSI combination is able to recover experimental values quite well even for a small basis set. However, the DMRG method reveals that the active space could potentially be improved by not only considering the two electrons in the seven 5f-orbitals but also including C-N-pi and corresponding C-N-pi* orbitals.

Keywords: CASSCF; DMRG; electron correlation; actinides; uranium; tetravalent; coordination chemistry

  • Lecture (Conference)
    Theory Frontiers in Actinide Sciences, 02.-05.02.2020, Santa Fe, USA
  • Invited lecture (Conferences)
    XIIIth Workshop on Modern Methods in Quantum Chemistry, 02.-05.03.2020, Mariapfarr, Österreich

Permalink: https://www.hzdr.de/publications/Publ-31745
Publ.-Id: 31745


2D THz Optoelectronics

Mittendorff, M.; Winnerl, S.; Murphy, T. E.

The terahertz (THz) region of the electromagnetic spectrum spans the gap between optics and electronics and has historically suffered from paucity of optoelectronic devices, in large part because of inadequate optical materials that function in this spectral range. 2D materials, including graphene and a growing family of related van der Waals materials, have been shown to exhibit unusual optical and electrical properties that can enable diverse new applications in the THz regime. In this review, some of the unusual properties of 2D materials that make them promising for THz applications are explained, the recent work in the field of 2D THz optoelectronics is summarized, and the challenges and opportunities that await this promising new field are outlined.

Keywords: terahertz; 2D materials; optoelectronics; THz detectors; THz emitters; THz modulators

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Permalink: https://www.hzdr.de/publications/Publ-31744
Publ.-Id: 31744


Observation of strong magneto plasmonic nonlinearity in bilayer graphene discs

Chin, M. L.; Matschy, S.; Stawitzki, F.; Poojali, J.; Hafez, H. A.; Turchinovich, D.; Winnerl, S.; Kumar, G.; Myers-Ward, R. L.; Dejarld, M. T.; Daniels, K. M.; Drew, H. D.; Murphy, T. E.; Mittendorff, M.

Graphene patterned into plasmonic structures like ribbons or discs strongly increases the linear and nonlinear optical interaction at resonance. The nonlinear optical response is governed by hot carriers, leading to a red-shift of the plasmon frequency. In magnetic fields, the plasmon hybridizes with the cyclotron resonance, resulting in a splitting of the plasmonic absorption into two branches. Here we present how this splitting can be exploited to tune the nonlinear optical response of graphene discs. In the absence of a magnetic field, a strong pump-induced increase in on-resonant transmission can be observed, but fields in the range of 3 T can change the characteristics completely, leading to an inverted nonlinearity. A two temperature model is provided that describes the observed behavior well.

Keywords: magnetoplasmonics; graphene; nonlinear optics

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Permalink: https://www.hzdr.de/publications/Publ-31743
Publ.-Id: 31743


Highly Tunable Magnetic and Magnetotransport Properties of Exchange Coupled Ferromagnet/Antiferromagnet-based Heterostructures

Arekapudi, S. S. P. K.; Bülz, D.; Ganss, F.; Samad, F.; Radu, F.; Zahn, D. R. T.; Lenz, K.; Salvan, G.; Albrecht, M.; Hellwig, O.

Antiferromagnets (AFMs) with zero net magnetization are proposed as active elements in future spintronic devices. Depending on the critical thickness of the AFM thin films and the measurement temperature, bimetallic Mn-based alloys and transition metal oxide-based AFMs can host various coexisting ordered, disordered, and frustrated AFM phases. Such coexisting phases in the exchange coupled ferromagnetic (FM)/AFM-based heterostructures can result in unusual magnetic and magnetotransport phenomena. Here, we integrate chemically disordered AFM γ-IrMn3 thin films with coexisting AFM phases into complex exchange coupled MgO(001)/γ-Ni3Fe/γ-IrMn3/γ-Ni3Fe/CoO heterostructures and study the structural, magnetic, and magnetotransport properties in various magnetic field cooling states. In particular, we unveil the impact of rotating the relative orientation of the disordered and reversible AFM moments with respect to the irreversible AFM moments on the magnetic and magnetoresistance properties of the exchange coupled heterostructures. We further found that the persistence of AFM grains with thermally disordered and reversible AFM order is crucial for achieving highly tunable magnetic properties and multi-level magnetoresistance states. We anticipate that the introduced approach and the heterostructure architecture can be utilized in future spintronic devices to manipulate the thermally disordered and reversible AFM order at the nanoscale.

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Permalink: https://www.hzdr.de/publications/Publ-31742
Publ.-Id: 31742


Microbial interaction with and tolerance of radionuclides: underlying mechanisms and biotechnological applications

Lopez Fernandez, M.; Jroundi, F.; Ruiz. Fresneda, M. A.; Merroun, M. L.

Radionuclides (RN) generated by nuclear and civil industries are released in natural ecosystems and may have a hazardous impact on human health and the environment. RN polluted environments harbor different microbial species that become highly tolerant of these elements through mechanisms including biosorption, biotransformation, biomineralization and intracellular accumulation. Such microbial-RN interaction processes hold biotechnological potential for the design of bioremediation strategies to deal with several contamination problems. This paper, with its multidisciplinary approach, provides a state-of-the-art review of most research endeavors aimed to elucidate how microbes deal with radionuclides and how they tolerate ionizing radiations. In addition, the most recent findings related to new biotechnological applications of microbes in the bioremediation of radionuclides and in the long-term disposal of nuclear wastes are described and discussed.

Permalink: https://www.hzdr.de/publications/Publ-31741
Publ.-Id: 31741


Multisystem combined uranium resistance mechanisms and bioremediation potential of Stenotrophomonas bentonitica BII-R7: Transcriptomics and microscopic study

Pinel-Cabello, M.; Jroundi, F.; Lopez Fernandez, M.; Geffers, R.; Jarek, M.; Jauregui, R.; Link, A.; Vílchez-Vargas, R.; Merroun, M. L.

The potential use of microorganisms in the bioremediation of U pollution has been extensively described.
However, a lack of knowledge on molecular resistance mechanisms has become a challenge for the use of these technologies. We reported on the transcriptomic and microscopic response of Stenotrophomonas bentonitica BII-R7 exposed to 100 and 250 μM of U. Results showed that exposure to 100 μM displayed up-regulation of 185 and 148 genes during the lag and exponential phases, respectively, whereas 143 and 194 were down-regulated, out of 3786 genes (>1.5-fold change). Exposure to 250 μM of U showed up-regulation of 68 genes and down-regulation of 290 during the lag phase. Genes involved in cell wall and membrane protein synthesis, efflux systems and phosphatases were up-regulated under all conditions tested. Microscopic observations evidenced the formation of U-phosphate minerals at membrane and extracellular levels. Thus, a biphasic process is likely to occur: the increased cell wall would promote the biosorption of U to the cell surface and its precipitation as U-phosphate minerals enhanced by phosphatases. Transport systems would prevent U accumulation in the cytoplasm. These findings contribute to an understanding of how microbes cope with U toxicity, thus allowing for the development of efficient bioremediation strategies.

Permalink: https://www.hzdr.de/publications/Publ-31740
Publ.-Id: 31740


Zinc Oxide Defect Microstructure and Surface Chemistry Derived from Oxidation of Metallic Zinc: Thin-Film Transistor and Sensor Behavior of ZnO Films and Rods

Hoffmann, R. C.; Sanctis, S.; Liedke, M. O.; Butterling, M.; Wagner, A.; Schneider, J. J.

Zinc oxide thin films are fabricated by controlled oxidation of sputtered zinc metal films on a hotplate in air at temperatures between 250 and 450°C. The nanocrystalline films possess high relative densities and show preferential growth in (100) orientation. Integration in thin film transistors reveal moderate charge carrier mobilities as high as 0.2 cm2/(Vs). The semiconducting properties depend on the calcination temperature, whereby the best performance is achieved at 450 °C. The defect structure of the thin ZnO film can be tracked by Doppler-broadening positron-annihilation-spectroscopy as well as positron-lifetime studies. Comparably long positron lifetimes suggest interaction of zinc vacancies (VZn) with one or more oxygen vacancies (Vo) in larger structural entities. Such VO-VZn defect clusters act as shallow acceptors and thus reduce the overall electron conductivity of the film. The concentration of these defect clusters decreases at higher calcination temperatures as indicated by changes of the S and W parameters. Such zinc oxide films obtained by conversion of metallic zinc can be also used as seed-layers for solution-deposition of zinc oxide nanowires employing a mild microwave-assisted process. The functionality of the obtained nanowire arrays was tested in a UV sensor device. Best results with respect to sensor sensitivity are achieved with thinner seed layers for device construction.

Keywords: positron annihilation spectroscopy; ZnO; defects; Positronium

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Permalink: https://www.hzdr.de/publications/Publ-31739
Publ.-Id: 31739


Oxidation of amorphous HfNbTaTiZr high entropy alloy thin films prepared by DC magnetron sputtering

Hruška, P.; Lukáč, F.; Cichoň, S.; Vondráček, M.; Čížek, J.; Fekete, L.; Lančok, J.; Veselý, J.; Minárik, P.; Cieslar, M.; Melikhova, O.; Kmječ, T.; Liedke, M. O.; Butterling, M.; Wagner, A.

High entropy alloys represent a new type of materials with a unique combination of physical properties originating from the occurrence of single-phase solid solutions of numerous elements. The preparation of nanostructured or amorphous structure in a form of thin films promises increased effective surface and high intergranular diffusion of elements as well as a high affinity to oxidation. In this work, we studied HfNbTaTiZr thin films were deposited at room temperature by DC magnetron sputtering from a single bcc phase target. Films exhibit cellular structure (~100 nm) with fine substructure (~10 nm) made of round-shape amorphous clusters. Films composition is close to equimolar with slight Ti enrichment and without any mutual segregation of elements. Oxidation at the ambient atmosphere leads to the formation of Ti, Zr, Nb, Hf, and Ta oxide clusters in the film up to the depth of 200 – 350 nm out of the total film thickness of 1650 nm. Oxygen absorption takes place preferentially in the large vacancy clusters located in between the amorphous cluster aggregates. The dominant type of defect is small open volumes with a size comparable with vacancy. The distribution of these defects is uniform with depth and is not influenced by the presence of oxygen in the film.

Keywords: positron annihilation spectroscopy; high entropy alloys; defects; monovacancy; HfNbTaTiZr; sputtering

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Permalink: https://www.hzdr.de/publications/Publ-31738
Publ.-Id: 31738


Methodology for DNS Data-driven Machine Learning Bubble Drag Model and Its Integration to OpenFOAM

Tai, C.-K.; Evdokimov, I.; Schlegel, F.; Lucas, D.; Bolotnov, I.

This work aims to develop a two-phase DNS data-driven bubble drag model and to implement it into a multiphase flow CFD simulation. To accomplish the goal, a Tensorflow (TF)-OpenFOAM(OF) integration interface has been established. Such an interface is capable of calling and making machine learning model to predict a quantity of interest on the fly. A benchmark case for the bubble drag coefficient is proposed to validate the interface. A Feed forward neural network (FNN) approach was utilized to approximate the drag correlation (Tomiyama et al., 1998) using artificially generated data. Results of the integration showed good consistency in radial void fraction and velocity profiles. As the next step actual DNS bubble tracking datasets are used as a data source (Fang et al., 2017, Cambareri et al., 2019). The data segments where bubble have quasi-stable main-stream velocity were filtered out for drag coefficient calculation. The DNS-informed model predicts bubble drag coefficient by taking bubble Reynolds number (Re) and Eötvös number (Eo) as input to consider the effects from local fluid and bubble shape. The model is applied in a Euler-Euler two-phase flow simulation of a bubbly pipe flow in OF. The required closure terms, except the drag model, utilize the baseline model of Liao et al. (2020) The results of radial void fraction and velocity profiles are discussed and compared to a reference solution with the baseline model.

Keywords: DNS; bubbly flow; drag; machine learning

  • Lecture (Conference) (Online presentation)
    APS DFD Annual Meeting, 22.-24.11.2020, Chicago - online, USA
  • Contribution to proceedings
    APS DFD Annual Meeting, 22.-24.11.2020, Chicago - online, USA

Permalink: https://www.hzdr.de/publications/Publ-31737
Publ.-Id: 31737


Short-duration dynamic FDG PET imaging: Optimization and clinical application

Samimi, R.; Kamali-Asl, A.; Geramifar, P.; van den Hoff, J.; Rahmim, A.

We aimed to investigate whether short dynamic PET imaging started at injection, complemented with routine clinical acquisition at 60-min post-injection (static), can achieve reliable kinetic analysis.
Methods
Dynamic and static 18F-2-fluoro-2-deoxy-D-glucose (FDG) PET data were generated using realistic simulations to assess uncertainties due to statistical noise as well as bias. Following image reconstructions, kinetic parameters obtained from a 2-tissue-compartmental model (2TCM) were estimated, making use of the static image, and the time duration of dynamic PET data were incrementally shortened. We also investigated, in the first 2-min, different frame sampling rates, towards optimized dynamic PET imaging. Kinetic parameters from shortened dynamic datasets were additionally estimated for 9 patients (15 scans) with liver metastases of colorectal cancer, and were compared with those derived from full dynamic imaging using correlation and Passing–Bablok regression analyses.
Results
The results showed that by reduction of dynamic scan times from 60-min to as short as 5-min, while using static data at 60-min post-injection, bias and variability stayed comparable in estimated kinetic parameters. Early frame samplings of 5, 24 and 30 s yielded highest biases compared to other schemes. An early frame sampling of 10 s generally kept both bias and variability to a minimum. In clinical studies, strong correlation (r ≥ 0.97, P < 0.0001) existed between all kinetic parameters in full vs. shortened scan protocols.
Conclusions
Shortened 5-min dynamic scan, sampled as 12 × 10 + 6 × 30 s, followed by 3-min static image at 60-min post-injection, enables accurate and robust estimation of 2TCM parameters, while enabling generation of SUV estimates.

Keywords: Dynamic PET; Kinetic modelling; GATE; STIR; FDG PET

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Permalink: https://www.hzdr.de/publications/Publ-31736
Publ.-Id: 31736


Message from the Guest Editor of the 17th Multiphase Flow Conference Special Issue

Lucas, D.

Selected contributions of the 17th Multiphase Flow Conference at HZDR were published in a special issue of the Open Access Journal Experimental and Computational Multiphase Flow. In this contribution an overview on the conference and a short introduction to the single papers is given.

Keywords: multiphase flow; conference

  • Open Access Logo Abstract in refereed journal
    Experimental and Computational Multiphase Flow 3(2021)3, 137-138
    DOI: 10.1007/s42757-020-0087-x

Permalink: https://www.hzdr.de/publications/Publ-31735
Publ.-Id: 31735


Current status and developments of German curriculum-based residency training programmes in radiation oncology

Büttner, M.; Cordes, N.; Gauer, T.; Habermehl, D.; Klautke, G.; Micke, O.; Mäurer, M.; Sokoll, J.; Troost, E. G. C.; Christiansen, H.; Niyazi, M.

Purpose: The current status of German residency training in the field of radiation oncology is provided and compared to programmes in other countries. In particular, we present the DEGRO-Academy within the international context.
Methods: Certified courses from 2018 and 2019 were systematically assigned to the DEGRO-Curriculum, retrospectively for 2018 and prospectively for 2019. In addition, questionnaires of course evaluations were provided, answered by course participants and collected centrally.
Results: Our data reveal a clear increase in curriculum coverage by certified courses from 57.6% in 2018 to 77.5% in 2019. The analyses enable potential improvements in German curriculum-based education. Specific topics of the DEGRO-Curriculum are still underrepresented, while others decreased in representation between 2018 and 2019. It was found that several topics in the DEGRO-Curriculum require more attention because of a low DEGRO-curriculum coverage. Evaluation results of certified courses improved significantly with a median grade of 1.62 in 2018 to 1.47 in 2019 (p=0.0319).
Conclusion: The increase of curriculum coverage and the simultaneous improvement of course evaluations are promising with respect to educational standards in Germany. Additionally, the early integration of radiation oncology into medical education is a prerequisite for resident training because of rising demands on quality control and increasing patient numbers. This intensified focus is a requirement for continued high standards and quality of curriculum-based education in radiation oncology both in Germany and other countries.

Keywords: radiotherapy; radiation oncology; curriculum; training; evaluation; DEGRO

Permalink: https://www.hzdr.de/publications/Publ-31734
Publ.-Id: 31734


Magnetic shielding factor for artefact-free in-beam MR imaging during proton pencil beam irradiation

Semioshkina, E.; Gantz, S.; Hoffmann, A. L.

Introduction
First measurements with a research prototype system for in-beam MR imaging during proton pencil beam scanning (PBS) have shown that the dynamic magnetic fringe fields of the nearby PBS magnets interfere with the static MRI (B0 =0.22 T) field, causing image ghosting artefacts [1]. Passive magnetic shielding is a possible means of eliminating the artefacts by decoupling the MR and PBS magnetic fields. The aim of this study was to determine the shielding factor required for artefact-free MR imaging during PBS dose delivery.
Materials and Methods
The change in B0 magnitude (ΔB0) due to the PBS fringe field was measured with a magnetic field camera positioned in the MR isocenter both as function of (1) the radiation field size [range 4−40 cm] and (2) the distance between the MR isocenter and the PBS isocenter [range 0.3−2.3 m]. Furthermore, images of the ACR Small Phantom were acquired during dose delivery for (1) and (2), and the percent signal ghosting ratio (PSGR) was assessed to determine the maximum ΔB0 for which the ACR action criterion of ≤0.025 was met.
Results
The magnetic field camera measurements showed that the maximum ΔB0 was 5.66 μT in the worst-case scenario of the minimum distance between MRI and PBS isocenter (0.3 m) and maximum scanning field size (40 cm). For this scenario, the PSGR test passed at a field size of 1.2 cm. Here, the maximum ΔB0 was 0.27 μT. The PSGR test was only passed for field sizes of 4 and 12 cm at distances of 1.3 m and 2.3 m between PBS and MR isocenter, respectively. In both cases, the maximum ΔB0 was 0.28 μT. Hence, a minimum shielding factor of 5.66 μT/0.28 μT = 20.22 would be required for artefact-free MR imaging during PBS dose delivery.
Conclusion
The magnetic shielding factor required for artefact-free MR imaging during PBS dose delivery was experimentally determined for the in-beam MR imaging research prototype system.
References
[1] S. Gantz et al. 2020 Phys. Med. Biol, 65(21), 215014

  • Contribution to proceedings
    MR in RT Symposium 2021, 19.04.2021, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31733
Publ.-Id: 31733


Development of a proton bunch monitor for accurate particle therapy treatment verification

Permatasari, F.; Schellhammer, S.; Lutz, B.; Pausch, G.; Römer, K.; Wagner, A.; Weinberger, D.; Werner, R.-D.; Werner, T.; Kögler, T.

Treatment verification is expected to improve targeting precision in particle therapy. A promising technique to achieve this goal is the detection of prompt gamma rays emitted along the particle tracks inside the patient. The range of the particle beam can be inferred by determining the time distribution of these gamma-rays relative to the radio frequency of the accelerator, a method commonly referred to as Prompt Gamma-Ray Timing.

However, the translation of this method into a clinical setting is currently hindered by instabilities of the phase relation between the arrival of the proton bunches and the radio frequency of the accelerator. These instabilities include two effects, which have been studied at the clinical treatment facility of the University Proton Therapy Dresden. Firstly, a long-term drift of the proton bunch phase relative to the radio frequency in the order of several hundred picoseconds per hour was observed, which may be caused by small temperature changes in the cyclotron’s magnet resulting in magnetization variations in its iron parts. Secondly, strongly damped oscillations in the mean of measured prompt gamma-ray timing spectra with an amplitude in the order of few hundred picoseconds occur for about two seconds after each change of the particle energy during pencil beam scanning. This oscillation is caused by ramping the acceleration voltage back to its nominal value, which is reduced between energy layers to minimize the dark current of the accelerator and the resulting excess dose to the patient.

While the former effect is only of secondary importance for the treatment due to its comparably long time scale, the phase oscillation has a considerable negative impact on the accuracy of the Prompt Gamma-Ray Timing method, which has to detect time shifts in the order of a few picoseconds for the detection of millimeter range changes. Therefore, the development of a method to monitor the arrival time of the proton bunches independently from the accelerator radio frequency, a so-called proton bunch monitor, is crucial.

To this end, a bunch monitor prototype was developed consisting of scintillating fibers placed in the halo of the proton beam. The fibers were read out on both ends by silicon photomultipliers. A thick acrylic glass target with cylindrical air cavities of varying thickness and different tissue-equivalent inserts was irradiated with protons of clinically relevant energies and typical beam currents. The mean proton arrival time, determined from the time spectra of the proton bunch monitor, was used to correct the prompt gamma-ray timing spectra acquired by Ø2”x2”CeBr3 high-resolution scintillation detectors. This correction allowed to resolve differences in the prompt-gamma ray timing spectra acquired with the different cavities and inserts.

In conclusion, the developed proton bunch monitor was successfully integrated to the Prompt Gamma-Ray Timing method and is expected to enable the clinical application of this method for clinical treatment verification in particle therapy.

Keywords: particle therapy; treatment verification; prompt gamma; bunch monitor

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  • Lecture (Conference) (Online presentation)
    ANIMMA 2021, 21.-25.06.2021, Praha, Česká republika

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Permalink: https://www.hzdr.de/publications/Publ-31732
Publ.-Id: 31732


Numerical simulation of micro-crack leakage on steam generator heat transfer tube

Zhao, X.; Liao, Y.; Wang, M.; Zhang, K.; Su, G. H.; Tian, W.; Qiu, S.; Lucas, D.

Flashing is frequently encountered in nuclear power systems for example as leakage occurring on the steam generator (SG) heat transfer tubes. Pressurized primary coolant flows rapidly through the crack and flashes into vapor. The pressure relief rate and loss rate of coolant, which affects largely the safety of fission reactors, are determined by the flashing phase change process. Information about the flashing phenomenon is of significance for the leakage online monitoring system, which ensures the normal operation of steam generator (SG) and safety of the reactor when tube rupture accidents occur. In this research, steady-state and transient 3D flashing flow inside a short micro-crack channel in the heat transfer tube wall of SG have been studied using FLUENT. The cavitation model and evaporation-condensation model, in combination with both the mixture two-phase flow and the Eulerian two-fluid model, are adopted to simulate the flashing phenomenon. The real geometry and operating conditions of AP1000 nuclear system are adopted to reflect the reality leakage phenomenon in SG. Two types of micro-crack shape including axial crack and circumferential crack, which both can happen in the reality, are considered. The CFD results gained from five different models have been compared with experimental data, and good agreement is demonstrated.
The model comparison shows that the evaporation-condensation model behaves superior to the cavitation model in simulating the flashing phenomenon. Finally, the leakage rates are gained under different crack shapes, sub-cooling degrees and backpressures with the most accuracy scheme. In addition, two-phase choking flow phenomenon is simulated by changing backpressure of cracked tubes. The simulation results in this research could be good reference for leakage prediction of micro-crack in SG to improve the operation performance of SG and safety of the whole nuclear power system.

Keywords: micro-crack; SG; CFD; flash boiling; FLUENT

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Permalink: https://www.hzdr.de/publications/Publ-31731
Publ.-Id: 31731


Data for: Bonding Trends in Tetravalent Th–Pu Monosalen Complexes

Radoske, T.; März, J.; Patzschke, M.; Kaden, P.; Walter, O.; Schmidt, M.; Stumpf, T.

[AnCl2(salen)(Pyx)2] (H2salen=N,N′‐bis(salicylidene)ethylenediamine; Pyx=pyridine, 4‐methylpyridine, 3,5‐dimethylpyridine) + An(IV) with An=Th, U, Np, and Pu.

EA data, QC calculation results, NMR spectra and data analysis.

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Permalink: https://www.hzdr.de/publications/Publ-31730
Publ.-Id: 31730


Measurement of Ehrlich-Schwoebel barrier contribution to the self-organized formation of ordered surface patterns on Ge(001)

Myint, P.; Erb, D.; Zhang, X.; Wiegart, L.; Zhang, Y.; Fluerasu, A.; Headrick, R.; Facsko, S.; Ludwig, K.

Normal-incidence 1-keV Ar+ ion bombardment leads to amorphization and ultrasmoothing of Ge at room temperature, but at elevated temperatures the Ge surface remains crystalline and is unstable to the formation of self-organized nanoscale patterns of ordered pyramid-shaped pits. The physical phenomenon distinguishing the high-temperature patterning from room-temperature ultrasmoothing is believed to be a surface instability due to the Ehrlich-Schwoebel barrier for diffusing vacancies and adatoms, which is not present on the amorphous material. This real-time grazing-incidence small-angle x-ray scattering study compares smoothing of a prepatterned Ge sample at room temperature with patterning of an initially flat Ge sample at an elevated temperature. In both experiments, when the nanoscale structures are relatively small in height, the average kinetics can be explained by a linear theory. The linear theory coefficients, indicating surface stability or instability, were extracted for both experiments. A comparison between the two measurements allows estimation of the contribution of the Ehrlich-Schwoebel barrier to the self-organized formation of ordered nanoscale patterns on crystalline Ge surfaces.

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Permalink: https://www.hzdr.de/publications/Publ-31729
Publ.-Id: 31729


The role of computational methods for automating and improving clinical target volume definition

Unkelbach, J.; Bortfeld, T.; Cardenas, C. E.; Gregoire, V.; Hager, W.; Heijmen, B.; Jeraj, R.; Korreman, S. S.; Ludwig, R.; Pouymayou, B.; Shusharina, N.; Söderberg, J.; Toma-Dasu, I.; Troost, E. G. C.; Osorio, E. V.

Treatment planning in radiotherapy distinguishes three target volume concepts: the gross tumor volume (GTV), the clinical target volume (CTV), and the planning target volume (PTV). Over time, GTV definition and PTV margins have improved through the development of novel imaging techniques and better image guidance, respectively. CTV definition is sometimes considered the weakest element in the planning process. CTV definition is particularly complex since the extension of microscopic disease cannot be seen using currently available in-vivo imaging techniques. Instead, CTV definition has to incorporate knowledge of the patterns of tumor progression. While CTV delineation has largely been considered the domain of radiation oncologists, this paper, arising from a 2019 ESTRO Physics research workshop, discusses the contributions that medical physics and computer science can make by developing computational methods to support CTV definition. First, we overview the role of image segmentation algorithms, which may in part automate CTV delineation through segmentation of lymph node stations or normal tissues representing anatomical boundaries of microscopic tumor progression. The recent success of deep convolutional neural networks has also enabled learning entire CTV delineations from examples. Second, we discuss the use of mathematical models of tumor progression for CTV definition, using as example the application of glioma growth models to facilitate GTV-to-CTV expansion for glioblastoma that is consistent with neuroanatomy. We further consider statistical machine learning models to quantify lymphatic metastatic progression of tumors, which may eventually improve elective CTV definition. Lastly, we discuss approaches to incorporate uncertainty in CTV definition into treatment plan optimization as well as general limitations of the CTV concept in the case of infiltrating tumors without natural boundaries.

Keywords: Automatic image segmentation; Clinical target volume; Computational tumor growth models

Permalink: https://www.hzdr.de/publications/Publ-31728
Publ.-Id: 31728


Numerical modeling and simulation of reactive flow and transport processes in subsurface formations

Yuan, T.

Subsurface water-rock interactions involve the coupled phenomena of chemical reactions and fluid transport, in which the chemical reactions between minerals and water can cause mineral dissolution/precipitation and aqueous species adsorption/desorption. The subsurface reactive transport processes play an important role in the enhanced prediction of oil and gas migration in the petroleum reservoirs as well as radionuclides migration in the host rocks. Consequently, an efficient numerical model that can rigorously capture such coupled phenomena is thus essential to the optimized design of implementations for those addressed problems.
In this talk, we first present a 3D mathematical model that couples the Stokes-Brinkman equation and reactive transport model for modeling the coupled processes of reactive flow and transport in fractured porous media. The numerical experiments show that the proposed model can efficiently simulate the coupled processes of fluid flow, reactive transport, and alterations of rock properties in fractured porous media under both linear and radial flow. Secondly, we focus on radionuclides transport and retention in claystone formations using GeoPET analysis and reactive transport modeling. We propose an integrated upscaling workflow to predict effective diffusivity of radionuclides diffusion in the shaly facies of Opalinus clay based on the reconstructed multi-scale digital rocks. The GeoPET measurements provide analytical insights into spatial and temporal tracer distribution, which can be utilized to validate the numerical model. The combination of pore-scale reactivity and core scale transport modeling provides critical insight into the radionuclide migration heterogeneity. We discuss these results with a focus on upscaling strategies to the field scale of host rocks.

  • Invited lecture (Conferences) (Online presentation)
    Numerical simulation of subsurface flow, 25.09.2020, Beijing, China

Permalink: https://www.hzdr.de/publications/Publ-31727
Publ.-Id: 31727


Quantification of the Inconvenient Truths about the Circular Economy (CE) Digital Twinning of Very Large Systems

Bartie, N. J.; Reuter, M.

We discuss the limitations to material flows from recycling in the circular economy, using as a case the simulation-based analysis of the CdTe Photovoltaic cells. It is important to use a simulation basis for the analysis, since this permits the quantification of all material losses both in terms of exergy and energy simultaneously i.e. 1st and 2nd law of thermodynamics. Harmonizing this with the power supply flowing into the system and minimizing energy usage as well as exergy losses will maximize the resource efficiency.

  • Open Access Logo Contribution to external collection
    Dagmar Boedicker, Sebastian Jekutsch, Dietrich Meyer-Ebrecht: FIfF-Kommunikation 3/2020 Technologie und Ökologie, Bremen: FIfF e.V., 2020, 0938-3476, 43-48

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Permalink: https://www.hzdr.de/publications/Publ-31726
Publ.-Id: 31726


Radionuclide transport and retention at the core scale identified by GeoPET analysis and reactive transport modeling

Yuan, T.; Kulenkampff, J.; Bollermann, T.; Fischer, C.

Low-permeability Opalinus clay formations are considered as a potential host rock for the storage of high-level nuclear waste (Nagra 2002). The diffusion of dissolved species is the dominating transport process in this rock type (Van Loon et al. 2003). Stratification and spatial variability of composition cause anisotropic and heterogeneous diffusion patterns, which could significantly speed up diffusive transport compared to commonly assumed homogeneous conditions. Anisotropy of diffusive transport has been studied on oriented samples in diffusion cells and with positron emission tomography (Kulenkampff et al. 2016). The heterogeneity of the diffusive spreading is increased still further due to sandy layers and diagenetic carbonates, affecting the radionuclide migration behavior at the core scale.
Here, we parameterize a reactive transport model by using experimental and analytical data on Eu(III) sorption efficiency at the pore scale. The effective retention coefficients calculated at the pore scale serve as input values for the reactive transport simulation at the core scale. Diffusive transport model parametrization utilizes GeoPET/μCT results on the migration behavior of 22Na+ at the core scale. Numerical simulation is performed using an existing code (Yuan et al. 2019), which contains the reactive transport model for simulating reactive diffusion process at the core scale. The combination of pore-scale reactivity and core scale transport modeling provides critical insight into the radionuclide migration heterogeneity. We discuss these results with a focus on upscaling strategies to the field scale of host rocks.

  • Lecture (Conference) (Online presentation)
    InterPore 2020, 31.08.-04.09.2020, Qing Dao, China

Permalink: https://www.hzdr.de/publications/Publ-31725
Publ.-Id: 31725


Experimental investigation of a stopping proton beam in liquid water using MR imaging

Gantz, S.; Karsch, L.; Pawelke, J.; Schellhammer, S.; Uber, S.; Hoffmann, A. L.

Introduction
To date, proton therapy is hampered by the lack of reliable in-vivo real-time feedback on the beam range, profile and energy deposition. So far, no technique enables the determination of beam effects on images also showing anatomical information in 2D/3D with high temporal and spatial resolution. The aim of this study is to demonstrate the possibility of visualizing a stopping proton beam in water using MR imaging.
Materials & methods
An open 0.22 T MR scanner was combined with a static proton research beamline to acquire MR images during simultaneous proton beam irradiation. Proton beams with an energy of 190−225 MeV and current of 3−64 nA impinged centrally on a 20 cm PMMA range modulator and were stopped in a water-filled phantom placed inside a dedicated knee MR receiver coil. A variety of different MR pulse sequences including T1- and T2-weighted Spin Echo (SE), Turbo Spin Echo, spoiled and unspoiled T1-weighted Gradient Echo (GE), inversion recovery gradient echo (IRGE), FLASH, Scout and time-of-flight (TOF) Angio were used. For each sequence, coronal images were acquired both with and without irradiation.
Results
The unspoiled GE sequence exhibited a hyper-intense central line artefact that showed a beam energy and current dependent twist under irradiation. The spoiled GE, IRGE, FLASH, Scout and TOF Angio sequences showed hyper- or hypo-intense signatures in the images that varied with the expected range and mimicked the shape of a 2D dose profile. The intensity of the effects depends on the beam current. The beam range determined from the MR images agrees to the expected range within a few millimeters. No beam induced signal changes were observed in the SE sequences.
Conclusion
A stopping proton beam in liquid water can be visualized with MRI. The observed signatures are beam energy and range as well as beam current and dose dependent. The underlying physical principles and the transferability to non-liquid materials needs further investigation.

  • Lecture (Conference)
    8th MR in RT Symposium 2021, 19.04.2021, Heidelberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31724
Publ.-Id: 31724


Convection in Liquid Metal Batteries

Weier, T.; Horstmann, G. M.; Landgraf, S.; Nimtz, M.; Personnettaz, P.; Weber, N.

The quest for renewable energy sources entails an increasingly intermittent electricity supply.
Transmission grid updates can only partially account for balancing the resulting variations and large-scale stationary storage will gain importance in future energy landscapes dominated by volatile sources.
Today’s battery technologies were, with the notable exception of redox-flow batteries, mainly designed for and driven by mobile applications. Those prioritize properties (energy density, power rating) that are less important for stationary storage. Thus, battery technologies developed from the ground up to meet the needs of stationary storage have the potential to much better address the specifics of huge capacity installations.
Liquid metal batteries (LMBs) are a new technology for grid-scale energy storage. They consist of all liquid cells that operate with liquid metals as electrodes and molten salts as electrolytes. The liquids separate into three stably stratified layers by virtue of density and mutual immiscibility. This conceptually very simple and self-assembling structure has the unique advantage to allow for an easy scale-up at the cell level: single-cell cross sections can potentially reach several square-meters. Such cell sizes enable highly favourable and otherwise unattainable ratios of active to construction material because of the cubic scaling (volume) of the former and the quadratic scaling (surface) of the latter. The total costs should therefore largely be determined by those of the active materials.
The talk will start with a general introduction to LMBs and then focus on the fluid mechanics in these devices. Electric currents, magnetic fields, and heat and mass transfer are tightly coupled with the cells’ electrochemistry. First a number of fluid dynamic instabilities will be discussed in relation to operational safety. The remainder of the talk will deal with transport phenomena in the positive electrode. While transport in most modern battery systems is typically dominated by diffusion and migration in micrometer-scale liquid layers and solids, convection - with exception of the aforementioned redox-flow batteries - rarely plays a role. This is in stark contrast to LMBs were mediated by the fully liquid interior fluid flow can be driven by various mechanisms. The influence of solutal convection on the cycling behavior of a cell will be demonstrated. Electromagnetically induced convection can be used to improve mixing thereby mitigating diffusion overpotentials.

  • Invited lecture (Conferences) (Online presentation)
    Liquid Metal Technologies, 20.11.2020, Morelia, Mexiko

Permalink: https://www.hzdr.de/publications/Publ-31723
Publ.-Id: 31723


Accurate determination of quasi-particle electronic and optical spectra of anatase titanium dioxide

Sruthil Lal, S. B.; Devaraj, M.; Posselt, M.; Sharan, A.

The electronic structure and quasi-particle absorption spectra of anatase titanium dioxide has been calculated by employing state of the art density functional theory(DFT) and Many-Body Perturbation Theory methods(MBPT) within the framework of Hybrid Density Functional(HSE). GW methods are used in combination with Bethe-Salpeter Equation (BSE) to determine the Quasi Particle energy levels and the role of excitons in optical absorption spectra. Accurate optical and electronic band gap are determined from these methods. In addition to it an analysis of charge redistribution within the anatase unit cell is also presented within the PBE - DFT to analyze the orbital hybridization patterns and the character of chemical bonds.

Keywords: Anatase Titanium Oxide; Density Functional Theory; Electronic structure; Optical Spectra

  • AIP Conference Proceedings 2265(2020), 030375
    Online First (2020) DOI: 10.1063/5.0017111

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Permalink: https://www.hzdr.de/publications/Publ-31722
Publ.-Id: 31722


Tailoring Particle-enzyme Nanoconjugates for Biocatalysis at the Organic-organic Interface

Sun, Z.; Cai, M.; Hübner, R.; Ansorge-Schumacher, M. B.; Wu, C.

Nonaqueous Pickering emulsions (PEs) are a powerful platform for catalysis design, offering both a large interface contact and a preferable environment for water-sensitive synthesis. However, up to now, little progress has been made to incorporate insoluble enzymes into the nonaqueous system for biotransformation. Herein, we present biocatalytically active nonaqueous PEs, stabilized by particle-enzyme nanoconjugates, for the fast transesterification and esterification, and eventually for biodiesel synthesis. Our nanoconjugates are the hybrid biocatalysts tailor-made by loading hydrophilic Candida antarctica lipase B onto hydrophobic silica nanoparticles, resulting in not only catalytically active but highly amphiphilic particles for stabilization of a methanol-decane emulsion. The enzyme activity in these PEs is significantly enhanced, ca. 375-time higher than in the nonaqueous biphasic control. Moreover, the PEs can be multiply reused without significant loss of enzyme performance. With this proof‐of‐concept, we reasonably expect that our system can be expanded for many advanced syntheses using different enzymes in the future.

Keywords: biphasic biocatalysis; nonaqueous Pickering emulsions; solvent-free reactions; enzyme catalysis; nanoconjugates

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Permalink: https://www.hzdr.de/publications/Publ-31721
Publ.-Id: 31721


Mechanosynthesis of polymer-stabilized lead bromide perovskites: insight into the formation and phase conversion of nanoparticles

Jiang, G.; Erdem, O.; Hübner, R.; Georgi, M.; Wei, W.; Fan, X.; Wang, J.; Demir, H. V.; Gaponik, N.

The application of polymers to replace oleylamine (OLA) and oleic acid (OA) as ligands for perovskite nanocrystals is an effective strategy to improve their stability and durability especially for the solution-based processing. Herein, we report a mechanosynthesis of lead bromide perovskite nanoparticles (NPs) stabilized by partially hydrolyzed poly(methyl methacrylate) (h-PMMA) and high-molecular-weight highly-branched poly(ethylenimine) (PEI-25K). The as-synthesized NP solutions exhibited green emission centered at 516 nm, possessing a narrow full-width at half-maximum of 17 nm and as high photoluminescence quantum yield (PL QY) as 85%, while showing excellent durability and resistance to polar solvents, e.g., methanol. The colloids of polymer-stabilized NPs were directly processable to form stable and strongly-emitting thin films and solids, making them attractive as gain media. Furthermore, the roles of h-PMMA and PEI-25K in the grinding process were studied in depth. The h-PMMA can form micelles in the grinding solvent of dichloromethane to act as size-regulating templates for the growth of NPs. The PEI-25K with large amounts of amino groups induced significant enrichment of PbBr2 in the reaction mixture, which in turn caused the formation of CsPb2Br5-mPbBr23-Cs4PbBr6-nCsBr NPs. The presence of CsPbBr3-Cs4PbBr6-nCsBr NPs was responsible for the high PL QY, as the Cs4PbBr6 phase with a wide energy bandgap can passivate the surface defects of the CsPbBr3 phase. This work describes a direct and facile mechanosynthesis of polymer-coordinated perovskite NPs and promotes in-depth understanding of the formation and phase conversion for perovskite NPs in the grinding process.

Keywords: lead bromide perovskites; mechanosynthesis; polymer ligands; polymer micelles; poly(ethyleneimine)-i

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Permalink: https://www.hzdr.de/publications/Publ-31720
Publ.-Id: 31720


Nonlinear IR and THz Spectroscopy of Semiconductor Nanowires

Helm, M.; Fotev, I.; Balaghi, L.; Lang, D.; Rana, R.; Winnerl, S.; Schneider, H.; Dimakis, E.; Pashkin, A.

We report nonlinear charge-carrier response in GaAs/InGaAs core/shell nanowires that are driven by intense THz pulses. In the first experiment, half-cycle THz pulses emitted from an organic DSTMS crystal lead to a red-shift of the plasmon Peak indicating intervalley transfer of the electrons. In the second experiment, a single, highly electron doped nanowire is investigated by scattering near-field infrared microscopy using intense free-electron laser (FEL) pulses. Here the observed red shift of the mid-infrared plasma resonance depends on the pulse energy and can be explained by heating the electron system in the nonparabolic conduction band.

Keywords: nanowire; THz; infrared; free-electron laser; near-field microscopy; nonlinear

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  • Invited lecture (Conferences) (Online presentation)
    45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2020), 08.-13.11.2020, Buffalo, USA
  • Contribution to proceedings
    45th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2020), 08.-13.11.2020, Buffalo, USA
    DOI: 10.1109/IRMMW-THz46771.2020.9370834
  • Invited lecture (Conferences) (Online presentation)
    EMRS Spring Meeting, 31.05.-04.06.2021, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-31719
Publ.-Id: 31719


Data for: Nonlinear losses in magnon transport due to four-magnon scattering

Hula, T.; Schultheiß, K.; Buzdakov, A.; Körber, L.; Bejarano, M.; Flacke, L.; Liensberger, L.; Weiler, M.; Shaw, J. M.; Nembach, H. T.; Faßbender, J.; Schultheiß, H.

We utilized the following methods in order to obtain the presented data: micro focused Brilluoin light scattering (BLS), micromagnetic simulations in MuMax3 and micro focused magneto-optical Kerr effect (MOKE). The experimental data were obtained on the sample which is labeled with: 'CoFe_WMI_6'. On that sample, we investigated the structures 'E1' and 'F1' which are essentially rectangular stripes (5 micrometer x 65 micrometer, thickness: 30 nm) out of Co25Fe75 alloy. The metadata for all measurements (including ALL parameters) are included in the uploaded primary data subdirectories. The references to the directory of the measured data within our local IT infrastructure are given along with the files themselves. All scripts that were used for data analysis (in Python) are included as well with a short description.

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Permalink: https://www.hzdr.de/publications/Publ-31718
Publ.-Id: 31718


Response of endothelial cells to gelatin-based hydrogels

Krüger-Genge, A.; Hauser, S.; Neffe, A. T.; Liu, Y.; Lendlein, A.; Pietzsch, J.; Jung, F.

Dysfunctional or incomplete endothelium on cardiovascular devices has been identified as key factor of thrombus formation. Therefore, the establishment of confluent endothelial cell (EC) monolayers is a challenge in cardiovascular device engineering. Previous studies revealed that arterial EC were able to endothelialize gelatin-based hydrogels. However, as EC differ markedly in their function dependent from their origin, this study investigated whether venous EC (HUVEC) also form a monolayer on gelatin-based hydrogels obtained by reacting gelatin with different molar ratios of lysine diisocyanate ethyl ester (using a 3-, 5- or 8-fold excess) exhibiting variations in their elastic properties. The density of adherent HUVEC on the soft hydrogel at 37 °C (G’ = 1.02 kPa, E = 1.1±0.3 kPa) was significantly lower than on the stiffer hydrogels (G’ = 2.515 and 5.02 kPa, E = 4.8±0.8 and 10.3±1.2 kPa). This was accompanied by increased matrix metalloproteases and stress fiber formation, while cell-to-cell contacts were comparable. The pattern of eicosanoids and cytokines corresponded to those results. The expression of pro-inflammatory markers COX-2, COX-1, and RAGE were slightly elevated, indicating a weak inflammation. The study revealed that hydrogels with higher moduli approached the status of a functionally-confluent HUVEC monolayer. The results indicate the promising potential especially of the hydrogels with higher G’ as biomaterials for implants foreseen for the venous system.

Keywords: endothelialization; gelatin-based hydrogel; substrate elasticity; HUVEC function; cell-material-interaction

Permalink: https://www.hzdr.de/publications/Publ-31717
Publ.-Id: 31717


Immunocompatibility and non-thrombogenicity of gelatin-based hydrogels

Krüger-Genge, A.; Tondera, C.; Hauser, S.; Braune, S.; Görs, J.; Roch, T.; Klopfleisch, R.; Neffe, A. T.; Lendlein, A.; Pietzsch, J.; Jung, F.

Immunocompatibility and non-thrombogenicity are important requirements for biomedical applications such as vascular grafts. Here, gelatin-based hydrogels formed by reaction of porcine gelatin with increasing amounts of lysine diisocyanate ethyl ester were investigated in vitro in this regard. In addition, potential adverse effects of the hydrogels were determined using the “Hen's egg test on chorioallantoic membrane” (HET-CAM) test and a mouse model. The study revealed that the hydrogels were immunocompatible, since complement activation was absent and a substantial induction of reactive oxygen species generating monocytes and neutrophils could not be observed in whole human blood. The density as well as the activation state of adherent thrombocytes was comparable to medical grade polydimethylsiloxane, which was used as reference material. The HET-CAM test confirmed the compatibility of the
hydrogels with vessel functionality since no bleedings, thrombotic events, or vessel destructions were observed. Only for the samples synthesized with the highest LDI amount the number of growing blood vessels in the CAM was comparable to controls and significantly higher than for the softer materials. Implantation into mice showed the absence of adverse or toxic effects
in spleen, liver, or kidney, and only a mild lymphocytic activation in the form of a follicular hyperplasia in draining lymph nodes (slightly increased after the implantation of the material prepared with the lowest LDI content. These results imply that candidate materials prepared with mid to high amounts of LDI are suitable for the coating of the blood contacting surface of cardiovascular implants.

Keywords: gelatin-based hydrogels; immune cells; platelets; in vitro testing; mouse model

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Permalink: https://www.hzdr.de/publications/Publ-31716
Publ.-Id: 31716


Synthese von neuartigen selektiven Histondeacetylase (HDAC)-Inhibitoren zur Entwicklung geeigneter ¹⁸F-markierter Radiotracer für die bildgebende Darstellung epigenetischer Prozesse in Tumoren

Clauß, O.; Schäker-Hübner, L.; Wenzel, B.; Toussaint, M.; Dukic-Stefanovic, S.; Ludwig, F.-A.; Gündel, D.; Teodoro, R.; Scheunemann, M.; Hansen, F. K.; Deuther-Conrad, W.; Brust, P.

Ziel:

Epigenetische Mechanismen wie die Methylierung und Acetylierung von Histonen regulieren die Genexpression auf Chromatin-Ebene. So beeinflusst der Grad der Acetylierung von Lysinresten der Histone die Zugänglichkeit der DNA und damit die Genexpression. HDACs sind in verschiedenen Tumorerkrankungen überexprimiert, woraus das Interesse an HDAC-Inhibitoren für die Therapie von Krebs resultiert. Das Ziel dieser Arbeit ist die Entwicklung neuer hochaffiner und selektiver fluortragender HDAC-Liganden, um HDAC1 und 2 in onkologischen Erkrankungen mittels PET darzustellen.
Methodik:
Basierend auf Tacedinalin wurden 10 fluorhaltige Derivate in bis zu 8 Synthesestufen hergestellt und ihre IC₅₀-Werte mittels eines biochemischen Enzymassays bestimmt. Von zwei Liganden mit hoher inhibitorischer Potenz und Selektivität für HDAC1 und 2 wurde HD70 ausgewählt und in einem Syntheseautomaten radiofluoriert. Zur biologischen Charakterisierung von [¹⁸F]HD70 wurden Untersuchungen in vitro und in vivo in der Maus durchgeführt.
Ergebnisse:
HD70 mit einem PAMBA-Linker (p-Aminomethylbenzoesäure) zeigt eine hohe inhibitorische Aktivität gegenüber HDAC1 (IC₅₀: 4,8 nM) und HDAC2 (IC₅₀: 39,9 nM). Die Radiosynthese von [¹⁸F]HD70 aus einem 2-Brompropionylpräkursor erfolgte automatisiert in zwei Stufen mit einer radiochemischen Ausbeute von 1 %. Die PET- und Metabolitenuntersuchungen in CD-1-Mäusen zeigten, dass der Radiotracer [¹⁸F]HD70 die Blut-Hirn-Schranke passiert (SUV5 min: 0,24). Allerdings betrug der Anteil an intaktem Tracer im Hirn nach 30 min nur 25 %.
Schlussfolgerungen:
Durch den hohen Anteil an hirngängigen Radiometaboliten wird [¹⁸F]HD70 für weitergehende Untersuchungen als ungeeignet eingestuft. Die erhaltenen Ergebnisse werden in das Design metabolisch stabilerer HDAC-Inhibitoren einfließen.

Keywords: Histondeacetylase-Inhibitor; Histondeacetylase 1; Positron-Emissions-Tomographie; Radiofluorierung; HDAC; PET; HDAC1

  • Lecture (Conference) (Online presentation)
    DGN-Kongress 2021, 14.-17.04.2021, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31715
Publ.-Id: 31715


Bonding Trends in Tetravalent Th–Pu Monosalen Complexes

Radoske, T.; März, J.; Patzschke, M.; Kaden, P.; Walter, O.; Schmidt, M.; Stumpf, T.

We report the synthesis of three complex series of the form [AnCl₂(salen)(pyx)₂] (H₂salen = N,N’-bis(salicyl¬idene)ethylene-diamine; Pyx = pyridine, 4-methylpyridine, 3,5-dimethylpyridine) with tetravalent early actinides (An = Th, U, Np, Pu) with the goal to elucidate the affinity of these heavy elements for small neutral N-donor molecules. Structure determination via single-crystal XRD and characterization of bulk powders with infrared spectroscopy reveal isostructurality within each respective series and the same complex conformation in all reported structures. While the trend of interatomic distances for An–Cl and An–N (imine nitrogen of salen or pyridyl nitrogen of Pyx) were found to reflect an ionic behaviour, the trend of the An–O distances can only be described with additional covalent interactions for all elements heavier than thorium. All experimental results are supported by quantum chemical calculations, which confirm the mostly ionic character in the An–N and An–Cl bonds, as well as the highest degree of covalency of the An–O bonds. Structurally, the calculations indicate just minor electronic or steric effects of the additional Pyx substituents on the complex properties.

Keywords: tetravalent actinide; salen; covalency; pyridine; bonding analysis; thorium; uranium; neptunium; plutonium

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Permalink: https://www.hzdr.de/publications/Publ-31714
Publ.-Id: 31714


"CFD-grade" Experimental data for Solid-liquid Flow in a Stirred Tank

Sommer, A.-E.; Rox, H.; Eckert, K.; Shi, P.; Rzehak, R.

A solid-liquid flow in stirred tanks occurs frequently in different branches of process engineering where particles need to be suspended in a liquid. Computational Fluid Dynamics (CFD) simulations of this type of flow on industrial scales are feasible if the closure models implemented therein are appropriate. A large number of closure models exist but, due to a lack of data sources for validation, no systematic assessment of these different models has appeared so far. The present dataset aims to accumulate a comprehensive ''CFD-grade'' database based on experiments on single-phase and two-phase flows in a standardized stirred tank with a diameter of 90 mm. The velocity fields of the liquid phase (deionized water) and, in the two-phase case, the solid phase were measured with Particle Image Velocimetry (PIV) and Particle Shadow Velocimetry (PSV), respectively. The experiments cover a range of parameters to achieve an extensive database. A narrow particle distribution of nearly neutrally buoyant particles (polyethylene spheres), as well as heavy particles (glass spheres) in suspension, are considered over a range of particle diameters (63µm-500µm), solid volume fractions (0.025 vol% - 0.1vol%), as well as impeller rotation speeds (650rpm - 1500rpm). The transient flow field on the plane midway between two baffles was recorded over 50 impeller rotations to achieve statistical significance. The time-averaged (or angle-resolved) mean and fluctuation velocities were then obtained by averaging the transient data in the laboratory frame of reference (or the frame of reference rotating with the impeller). The data is organized and analyzed as described in the corresponding journal publication "Solid-liquid Flow in Stirred Tanks: ”CFD-grade” Experimental Investigation".

Keywords: stirred tanks; solid-liquid flow; Particle Image Velocimetry (PIV); Particle Shadow Velocimetry (PSV); "Computational Fluid Dynamics (CFD)-grade" database

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Permalink: https://www.hzdr.de/publications/Publ-31713
Publ.-Id: 31713


Terahertz magneto-optical investigation of quadrupolar spin-lattice effects in magnetically frustrated Tb2Ti2O7

Amelin, K.; Alexanian, Y.; Nagel, U.; Rõõm, T.; Robert, J.; Debray, J.; Simonet, V.; Decorse, C.; Wang, Z.; Ballou, R.; Constable, E.; de Brion, S.

Condensed matter magneto-optical investigations can be a powerful probe of a material's microscopic magnetoelectric properties. This is because subtle interactions between electric and magnetic multipoles on a crystal lattice show up in predictable and testable ways in a material's optical response tensor, which dictates the polarization state and absorption spectrum of propagating electromagnetic waves. Magneto-optical techniques are therefore strong complements to probes such as neutron scattering, particularly when spin-lattice coupling effects are present. Here we perform a magneto-optical investigation of vibronic spin-lattice coupling in the magnetically frustrated pyrochlore Tb2Ti2O7. Coupling of this nature involving quadrupolar mixing between the Tb3+ electronic levels and phonons in Tb2Ti2O7 has been a topic of debate for some time. This is particularly due to its implication for describing the exotic spin-liquid phase diagram of this highly debated system. A manifestation of this vibronic effect is observed as splitting of the ground and first excited crystal field doublets of the Tb3+ electronic levels, providing a fine structure to the absorption spectra in the terahertz (THz) frequency range. In this investigation, we apply a static magnetic field along the cubic [111] direction while probing with linearly polarized THz radiation. Through the Zeeman effect, the magnetic field enhances the splitting within the low-energy crystal field transitions revealing new details in our THz spectra. Complementary magneto-optical quantum calculations including quadrupolar terms show that indeed vibronic effects are required to describe our observations at 3 K. A further prediction of our theoretical model is the presence of a novel magneto-optical birefringence as a result of this vibronic process. Essentially, spin-lattice coupling within Tb2Ti2O7 may break the optical isotropy of the cubic system, supporting two different electromagnetic wave propagations within the crystal. Together our results reveal the significance of considering quadrupolar spin-lattice effects when describing the spin-liquid ground state of Tb2Ti2O7. They also highlight the potential for future magneto-optical investigations to probe complex materials where spin-lattice coupling is present and reveal new magneto-optical activity in the THz range.

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Permalink: https://www.hzdr.de/publications/Publ-31712
Publ.-Id: 31712


Broad Beam-Induced Fragmentation and Joining of Tungsten Oxide Nanorods: Implications for Nanodevice Fabrication and the Development of Fusion Reactors

Rajbhar, M. K.; Möller, W.; Satpati, B.; Manju, U.; Chaudhary, Y. S.; Chatterjee, S.

In this work, for the first time, fragmentation and joining of tungsten oxide (WO3) nanorods induced by a broad ion beam are reported. Although at low energy (5 keV) and moderate ion fluence, nanorods fragment into smaller pieces along the length, at higher ion energies (50-100 keV), a contrary process occurs, which leads to the joining of the nanorods. A state-of-the-art ion-solid interaction simulation, namely, TRI3DYN, has been invoked to explore the possible mechanisms that reveal subtle contributions of surface defects, ion-beam mixing, and sputtering. High-resolution electron microscopy, photoluminescence study, and X-ray photoelectron spectroscopy support the observed results and proposed mechanisms. Such modifications have interesting effects on the electrical conductivity of the nanorod assembly. The change in sample color upon ion irradiation from initial white to yellow, light blue, deep blue, light green, and cyan shows an excellent and reversible chromatic response of tungsten oxide nanorods to irradiation. Such a property can be exploited to fabricate radiation sensors. The fragmentation and joining at different energy scales have essential implications in nanodevice fabrication through the bottom-up approach as well as for the development of fusion reactors.

Keywords: electrical conductivity; fusion reactor material; ion irradiation; nanofragmentation; nanojoining; radiation sensor; tungsten oxide nanorods; wettability

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Permalink: https://www.hzdr.de/publications/Publ-31710
Publ.-Id: 31710


Imaging of the human CB2 receptors in the brain with PET: Development and biological evaluation of [18F]JHU94620-d8

Gündel, D.; Teodoro, R.; Deuther-Conrad, W.; Toussaint, M.; Bormans, G.; Brust, P.; Moldovan, R.-P.

2Laboratory for Radiopharmacy, KU Leuven, Leuven, Belgium
Introduction: In pathological conditions, the up-regulation of cannabinoid receptors type 2 (CB2) receptors has been reported in association with traumatic brain injury (TBI), neurodegeneration and cancer.[1] Up to date, only [11C]NE40 was evaluated in human subjects as PET tracer for the CB2 receptors. Recently, we reported the development of [18F]JHU94620, a highly affine and selective 18F-labeled CB2 radiotracer (Ki(hCB2) = 0.4 nM, Ki(hCB1) = 380 nM). However, this radioligand suffers from low metabolic stability in-vivo (36% intact tracer detected at 30 min p.i. in brain of CD1 mice).[2] Here, we describe the development of the deuterated analogues [18F]JHU94620-d4 and [18F]JHU94620-d8 as well as their in vitro and in-vivo evaluation in rats.
Methods: The precursors for radiofluorination were obtained by coupling 4,5-dimethylthiazol-ylidene-2,2,3,3-tetramethylcyclopropane-1-carboxamide with either d4 or d8 1,4-butanediol-bistosylate. The radiosynthesis of the deuterated [18F]JHU94620 analogues was performed in presence of Kryptand K2.2.2. and K2CO3. The metabolic stability of the new tracers was evaluated at 30 min p.i. in plasma, brain and spleen of healthy CD1 mice. The affinity and specificity toward the CB2 receptor was evaluated by in vitro autoradiography and binding experiments. Additionally, we evaluated the [18F]JHU94620-d8 uptake in vivo by PET-studies into the spleen of healthy rats and in a rat model overexpressing the hCB2 in the right striatum.[3]
Results: [18F]JHU94620-d4 and -d8 were obtained in moderate radiochemical yields of about 10% and high radiochemical purities (>99%). Preliminary results revealed a considerable improved metabolic stability of both deuterated [18F]JHU94620 analogues with 80% intact tracer in the brain at 30 min. p.i. in mice. In-vitro evaluation of [18F]JHU94620-d8 revealed a KD(rCB2) = 0.36 nM (SPRD rats spleen homogenates) and KD(hCB2) = 2.72 nM (hCB2-CHO cell membrane homogenate) as well as specific binding in mice and rat spleen autoradiography. PET studies with [18F]JHU94620-d8 revealed a rCB2 specific spleen uptake, which could be blocked by the CB2 agonist GW405833. Furthermore, a specific and reversible uptake of [18F]JHU94620-d8 revealed a constant SUV of 6.7±0.3 from 6 to 60 min p.i. in the rat model overexpressing the hCB2 in the right striatum with a high signal to background ratio shown by a SUVr (right striatum-to-cerebellum) of 43±7at 60 min p.i..
Conclusion: [18F]JHU94620-d8 is a new PET tracer with improved metabolic stability and excellent ability to image the CB2 receptors in-vivo. Its further evaluation is underway.

  • Lecture (Conference) (Online presentation)
    59. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 14.-17.04.2021, Hybridveranstaltung, Deutschland
  • Poster
    59. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 14.-17.04.2021, Hybridveranstaltung, Germany

Permalink: https://www.hzdr.de/publications/Publ-31709
Publ.-Id: 31709


Hypofractionated Versus Standard Fractionated Radiotherapy in Patients With Early Breast Cancer or Ductal Carcinoma In Situ in a Randomized Phase III Trial: The DBCG HYPO Trial

Offersen, B. V.; Alsner, J.; Nielsen, H. M.; Jakobsen, E. H.; Nielsen, M. H.; Krause, M.; Stenbygaard, L.; Mjaaland, I.; Schreiber, A.; Kasti, U.-M.; Overgaard, J.

PURPOSE Given the poor results using hypofractionated radiotherapy for early breast cancer, a dose of 50 Gy in 25 fractions (fr) has been the standard regimen used by the Danish Breast Cancer Group (DBCG) since 1982. Results from more recent trials have stimulated a renewed interest in hypofractionation, and the noninferiority DBCG HYPO trial (ClincalTrials.gov identifier: NCT00909818) was designed to determine whether a dose of
40 Gy in 15 fr does not increase the occurrence of breast induration at 3 years compared with a dose of 50 Gy in 25 fr.

PATIENTS AND METHODS One thousand eight hundred eighty-two patients .40 years of age who underwent breast-conserving surgery for node-negative breast cancer or ductal carcinoma in situ (DCIS) were randomly assigned to radiotherapy at a dose of either 50 Gy in 25 fr or 40 Gy in 15 fr. The primary end point was 3-year grade 2-3 breast induration assuming noninferiority regarding locoregional recurrence.

RESULTS A total of 1,854 consenting patients (50 Gy, n 5937; 40 Gy, n 5917) were enrolled from 2009-2014 from eight centers. There were 1,608 patients with adenocarcinoma and 246 patients with DCIS. The 3-year rates of induration were 11.8% (95% CI, 9.7% to 14.1%) in the 50-Gy group and 9.0% (95% CI, 7.2% to 11.1%) in the 40-Gy group (risk difference, 22.7%; 95% CI, 25.6% to 0.2%; P 5 .07). Systemic therapies and radiotherapy boost did not increase the risk of induration. Telangiectasia, dyspigmentation, scar appearance, edema, and pain were detected at low rates, and cosmetic outcome and patient satisfaction with breast appearance were high with either no difference or better outcome in the 40-Gy cohort compared with the 50-Gy cohort. The 9-year risk of locoregional recurrence was 3.3% (95% CI, 2.0% to 5.0%) in the 50-Gy group and 3.0% (95% CI, 1.9% to 4.5%) in the 40-Gy group (risk difference, 20.3%; 95% CI, 22.3% to 1.7%). The 9-year overall survival was 93.4% (95% CI, 91.1% to 95.1%) in the 50-Gy group and 93.4% (95% CI, 91.0% to 95.2%)
in the 40-Gy group. The occurrence of radiation-associated cardiac and lung disease was rare and not influenced by the fractionation regimen.

CONCLUSION Moderately hypofractionated breast irradiation of node-negative breast cancer or DCIS did not result in more breast induration compared with standard fractionated therapy. Other normal tissue effects were minimal, with similar or less frequent rates in the 40-Gy group. The 9-year locoregional recurrence risk was low.

Permalink: https://www.hzdr.de/publications/Publ-31708
Publ.-Id: 31708


Underground experimental study finds no evidence of low-energy resonance in the 6Li(p,γ)7Be reaction

Piatti, D.; Chillery, T.; Depalo, R.; Aliotta, M.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Cavanna, F.; Ciani, G. F.; Corvisiero, P.; Csedreki, L.; Davinson, T.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fiore, E. M.; Formicola, A.; Fülöp, Z.; Gervino, G.; Gnech, A.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Kochanek, I.; Lugaro, M.; Marcucci, L. E.; Marigo, P.; Masha, E.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Paticchio, V.; Perrino, R.; Prati, P.; Schiavulli, L.; Stöckel, K.; Straniero, O.; Szücs, T.; Takács, M. P.; Zavatarelli, S.

The astrophysical 6Li(p,γ)7Be reaction occurs during Big Bang nucleosynthesis and the pre-main sequence and main sequence phases of stellar evolution. The low-energy trend of its cross section remains uncertain, since different measurements have provided conflicting results. A recent experiment reported a resonancelike structure at center-of-mass energy 195 keV, associated to a positive-parity state of 7Be. The existence of such resonance is still a matter of debate. We report a new measurement of the 6Li(p,γ)7Be cross section performed at the Laboratory for Underground Nuclear Astrophysics, covering the center-of-mass energy range E=60–350 keV. Our results rule out the existence of low-energy resonances. The astrophysical S-factor varies smoothly with energy, in agreement with theoretical models.

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Permalink: https://www.hzdr.de/publications/Publ-31707
Publ.-Id: 31707


Optimization of multi-group energy structures for diffusion analyses of sodium-cooled fast reactors assisted by simulated annealing – Part I: methodology demonstration

Di Nora, V. A.; Fridman, E.; Nikitin, E.; Bilodid, Y.; Mikityuk, K.

This study presents an approach to the selection of optimal energy group structures for multi-group nodal diffusion analyses of Sodium-cooled Fast Reactor cores. The goal is to speed up calculations, particularly in transient calculations, while maintaining an acceptable accuracy of the results.
In Part I of the paper, possible time-savings due to collapsing of energy groups are evaluated using 24-group energy structure as a reference. Afterwards, focusing on energy structures with a number of groups leading to significant calculation speedups, optimal grid configurations are identified. Depending on a number of possible energy grid configurations to explore, the optimization is conducted by either a direct search or applying the simulated annealing method. Speedup and optimization studies are performed on a selected case of the Superphénix static neutronic benchmark by using the nodal diffusion DYN3D code. The results demonstrate noticeable improvements in DYN3D performance with a marginal deterioration of the accuracy.

Keywords: Serpent; XS condensation; energy structure optimization; simulated annealing

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Permalink: https://www.hzdr.de/publications/Publ-31706
Publ.-Id: 31706


A Molecular Octafluoridoneptunate(IV) anion in (NH₄)₄[NpF₈] and Theoretical Investigations of the [MF₈]₄-System (M = Th - Bk)

Scheibe, B.; Patzschke, M.; März, J.; Conrad, M.; Kraus, F.

Olive-green single crystals of ammonium octafluoridoneptunate(IV), (NH₄)₄[NpF₈], were obtained by converting NpO₂ to a green neptunium tetrafluoride hydrate with hydrofluoric acid and subsequent treatment of the fluoride with an aqueous NH₄F solution. The crystal structure of the compound was determined by single-crystal X ray diffraction and observed to be isotypic to the uranium analogue. In (NH₄)₄[NpF₈], molecular [NpF₈]⁴‾ anions, which can either be described as a distorted square-antiprism or a bicapped trigonal prism, are present which are bound to the NH₄⁺ ions via N−H∙∙∙F hydrogen bonds. Quantum-chemical calculations of [MF₈]⁴‾ anions show that the M−F bonds are highly ionic and the energy differences between different ligand arrangements likely can be overcome by lattice energies of different crystal structures in the solid state.

Keywords: actinide; density functional calculations; neptunium; fluorine; single-crystal X-ray diffraction

Permalink: https://www.hzdr.de/publications/Publ-31705
Publ.-Id: 31705


HIM FIBID dataset for Superconducting properties of in-plane W-C nanowires grown by He+ Focused Ion Beam Induced Deposition

Hlawacek, G.
Project Member: Orus, Pablo

HIM images and NPVE dataset created during the preparation of the W(CO)6 nanowires.

Keywords: helium ion microscopy; focused ion beam induced deposition

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Permalink: https://www.hzdr.de/publications/Publ-31704
Publ.-Id: 31704


Superconducting properties of in-plane W-C nanowires grown by He+ Focused Ion Beam Induced Deposition

Orús, P.; Córdoba, R.; Hlawacek, G.; de Teresa, J. M.

Focused Ion Beam Induced Deposition (FIBID) is a nanopatterning technique that makes use of a focused beam of charged ions to decompose a gaseous precursor. So far, the flexible patterning capabilities of FIBID have been widely exploited in the fabrication of superconducting nanostructures, using the W(CO) 6 precursor mostly in combination with a focused beam of Ga+ ions. Here, the fabrication and characterization of superconducting in-plane tungsten-carbon (W-C) nanostructures by He+ FIBID of the W(CO)6 precursor is reported. A virtually unattainable for Ga+ FIBID patterning resolution of 10 nm has been achieved. When the nanowires are patterned with widths of 20 nm and above, the deposited material is superconducting below 3.5 – 4 K. In addition, 60 and 90 nm-wide nanostructures have been found to sustain long-range controlled non-local superconducting vortex transfer along 3 μm. Overall, these findings strengthen the capabilities of He+ FIBID of W-C in the growth and patterning of in-plane superconducting nanodevices.

Keywords: superconductivity; Helium Ion Microscopy; FIBID; nanowires; vortexdynamics; electrical transport properties

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Permalink: https://www.hzdr.de/publications/Publ-31703
Publ.-Id: 31703


Evolution of cast iron- and copper- corrosion in "400 day-bentonite-microcosms"

Sushko, V.; Dressler, M.; Neubert, T.; Kühn, L.; Cherkouk, A.; Schierz, A.; Matschiavelli, N.

Copper and cast iron are potential materials for the storage canisters of high-level radioactive waste. We designed slurry-experiments for analyzing the microbial influence on the corrosion process of these metals. These slurry experiments contain the Bavarian B25 bentonite, synthetic Opalinus Clay pore water or diluted cap rock solution as well as copper- or cast iron plates in various combinations. During an incubation time of 400 days under anaerobic conditions at 37 °C cast iron plates corrode very fast. The respective metal surfaces show the formation of iron oxides and –carbonates which could form a passivating film that protects the cast iron from further corrosion.

  • Open Access Logo Lecture (Conference) (Online presentation)
    iCross annual meeting 2020, 25.-26.11.2020, Dresden-Webinar, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31702
Publ.-Id: 31702


Solid-liquid Flow in Stirred Tanks: "CFD-grade" Experimental Investigation

Sommer, A.-E.; Rox, H.; Eckert, K.; Shi, P.; Rzehak, R.

Computational Fluid Dynamics (CFD) simulations of the solid-liquid flow in stirred tanks are feasible with appropriate closure models. However, no systematic assessment of different models have appeared because of lacking validation data. The present study accumulates a "CFD-grade" database on single-phase and two-phase flows experiments in a stirred tank (diameter=90mm). The velocity fields of the liquid and the solid phase are measured with Particle Image Velocimetry and Particle Shadow Velocimetry, respectively. The experiments cover a range of parameters as density ratio (ρS / ρL = 1.1...2.5), particle diameter (63 μm...500 μm), solid volume fraction (0.025vol%...0.1vol%) and impeller rotation speed (650rpm...1500 rpm). The mean and fluctuating liquid and solid velocities are obtained as time and angle-resolved averaging, as well as the local solid fraction. The experimental data of the single phase flow is compared with CFD simulations and show a good predictions. A systematic assessment of CFD models for solid-liquid flows will appear as a sequel.

Keywords: stirred tanks; solid-liquid flow; Particle Image Velocimetry (PIV); Particle Shadow Velocimetry (PSV); "Computational Fluid Dynamics (CFD)-grade" database

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Permalink: https://www.hzdr.de/publications/Publ-31701
Publ.-Id: 31701


Cd2+ incorporation in small pores LEV/ERI intergrown zeolites: a multi-methodological study

Cametti, G.; Scheinost, A.; Churakov, S. V.

Small pores zeolites are successfully employed as catalysts, sorbents and molecular sieves. Their physiochemical properties can be improved by modifying their extraframework (EF) cation content via ion exchange. In this study, we investigate the crystal structure of a Cd-exchanged levyne (LEV) intergrown with erionite (ERI) by combining Single Crystal X-ray Diffraction (SCXRD), Molecular Dynamic simulations (MD) and Extended X-ray Absorption Fine- Structure analysis spectroscopy (EXAFS). Data obtained from the different techniques, consistently indicated that Cd2+ distribute in an almost ordered fashion in LEV. In contrast, strong disorder of the EF species (Cd2+ and H2O) is observed in the ERI cavities. In the latter, Cd2+ form aqueous complexes that are more mobile in comparison towith respect Cd2+ in LEV, where it bonds to H2O and framework-oxygen atoms. The formation of Cd-clusters is excluded based on EXAFS analysis. Finally, to discriminate between thermal and static disorder, we proposed a new approach based on a combined MD and geometry optimization analysis.

Keywords: zeolite; levyne; MD simulations; DFT; XRD; EXAFS; ROBL

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Permalink: https://www.hzdr.de/publications/Publ-31700
Publ.-Id: 31700


Ideen zur Untersuchung der MIC Beständigkeit von vorgealterten Materialien

Raff, J.; Cherkouk, A.; Matschiavelli, N.; Sushko, V.; Dressler, M.

Neben abiotischen Faktoren können auch mikrobielle Prozesse einen Einfluss auf die Langzeitsicherheit eines nuklearen Endlagers haben. Darum wird aktuell im Rahmen des Projekts iCROSS die mikrobiellen Diversität in dem Verfüllmaterial Bentonit untersucht und die mikrobielle Aktivität mittels Mikrokosmosexperimenten bestimmt. Weitere Experimente befassen sich außerdem mit der mikrobiell beeinflussten Korrosion von Behältermaterialien. Letzteres ist auch von hoher Relevanz für andere technische Anlagen und Prozesse. Aus diesem Grund werden in dem Vortrag außerdem Möglichkeiten für weitere Projektideen aufgezeigt und diskutiert.

Keywords: Mikrobielle Diversität; nukleares Endlager; Bentonit; MIC

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  • Lecture (Conference) (Online presentation)
    DECHEMA/GfKORR Fachgruppensitzung „Mikrobielle Materialzerstörung und Materialschutz“ 27.10.2020, 27.10.2020, Online, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31699
Publ.-Id: 31699


The effect of four lanthanides onto a rat kidney cell line (NRK-52E) is dependent on the composition of the cell culture medium

Heller, A.; Pisarevskaja, A.; Bölicke, N.; Barkleit, A.; Bok, F.; Wober, J.

Lanthanide (Ln) exposure poses a serious health risk to animals and humans. In this study, we investigated the effect of 10-9 - 10-3 M La, Ce, Eu, and Yb exposure onto the viability of rat renal NRK-52E cells in dependence on Ln concentration, exposure time, and composition of the cell culture medium. Especially, the influence of fetal bovine serum (FBS) and citrate onto Ln cytotoxicity, solubility, and speciation was investigated. For this, in vitro cell viability studies using the XTT assay and fluorescence microscopic investigations were combined with solubility and speciation studies using TRLFS and ICP-MS, respectively. The theoretical Ln speciation was predicted using thermodynamic modeling. All Ln exhibit a concentration- and time-dependent effect on NRK-52E cells. FBS is the key parameter influencing both Ln solubility and cytotoxicity. We demonstrate that FBS is able to bind Ln3+ ions, thus, promoting solubility and reducing cytotoxicity after Ln exposure for 24 and 48 h. In contrast, citrate addition to the cell culture medium has no significant effect on Ln solubility and speciation nor cytotoxicity after Ln exposure for 24 and 48 h. However, a striking increase of cell viability is observable after Ln exposure for 8 h. Out of the four Ln elements under investigation, Ce is the most effective. Results from TRLFS and solubility measurements correlate well to those from in vitro cell culture experiments. In contrast, results from thermodynamic modeling do not correlate to TRLFS results, hence, demonstrating that big gaps in the database render this method, currently, inapplicable for the prediction of Ln speciation in cell culture media. Finally, this study demonstrates the importance and the synergistic effects of combining chemical and spectroscopic methods with cell culture techniques and biological methods.

Keywords: f-elements; speciation; cytotoxicity; XTT; time-resolved laser-induced fluorescence spectroscopy; thermodynamic modeling

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Permalink: https://www.hzdr.de/publications/Publ-31698
Publ.-Id: 31698


PIConGPU setup: PWFA simulations

Pausch, R.; Debus, A.; Steiniger, K.; Widera, R.

This is the PIConGPU source code and setup files for generating PWFA simulations. This setup was used to study wake elongation.

Keywords: PIConGPU; PWFA

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Permalink: https://www.hzdr.de/publications/Publ-31697
Publ.-Id: 31697


Operating system (OS) independent job configuration for image reconstruction at HEMERA

Bieberle, A.; Wagner, M.; Windisch, D.; Hampel, U.

The Institute of Fluid Dynamics at the HZDR operates ultrafast electron beam X-ray CT scanners, a.k.a. ROFEX-CT scanners, that are used to visualize rapidly moving two-phase gas-liquid scenarios in technical devices with an imaging rate of up to 8,000 images per second. This means, radiographic projections are acquired from different angular positions of the two-phase flow and reconstruction algorithms, e.g. filtered back projection or algebraic reconstruction technique, are applied to obtain a stack of cross-sectional images as a sequence of time. The scanners can be operated in single or dual-plane mode. The presentation highlights the construct that is developed to start OS-independent data reconstruction jobs at HEMERA.

Keywords: X-ray CT scanner; HPC

  • Lecture (others) (Online presentation)
    Seminar Series - Hardware and Numerics, 08.12.2020, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31696
Publ.-Id: 31696


Curium(III) and europium(III) as luminescence probes for plant cell (Brassica napus) interactions with potentially toxic metals

Moll, H.; Schmidt, M.; Sachs, S.

We have investigated the interaction of the actinide Cm(III) and its lanthanide homologue Eu(III) with cells of Brassica napus in suspension. This study combines biochemical techniques (plant cell response) with spectroscopic experiments to determine the chemical speciation of the metals in contact with the cells. Experiments conducted over a period of 7 d showed that B. napus cells were able to bioassociate both potentially toxic metals, with results confirming up to 0.58 µmol Eu/gfresh cells and 1.82 µmol Cm/gfresh cells at the lowest provided metal concentration. For Cm(III), a biosorption process could be identified as soon as 5 h post-exposure with 73±4% of the Cm(III) bioassociated. Additional luminescence spectroscopy results based on UV and site-selective excitation confirmed the existence of three Cm(III)/Eu(III), M(III), species in both the supernatants and cells. The findings detailed herein support that M(III) coordination to two kinds of carboxyl groups and phosphate groups.

Keywords: actinides; lanthanides; plant cells; laser spectroscopy; speciation

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Permalink: https://www.hzdr.de/publications/Publ-31695
Publ.-Id: 31695


mallocMC - Memory Allocator for Many Core Architectures

Widera, R.; Eckert, C.; Hübl, A.; Gruber, B. M.; Bastrakov, S.; Worpitz, B.; Grund, A.

This project provides a framework for fast memory managers on many core accelerators. It is based on alpaka to run on many different accelerators and implements the ScatterAlloc algorithm.

Keywords: CUDA; HIP; AMD; NVIDIA; memory allocation; many core; scatter alloc; C++

  • Software in external data repository
    Publication year 2020
    Programming language: C++
    System requirements: - OS: Linux/Windows/OSX - C++ 11 compiler - CUDA
    License: MIT
    Hosted on GitHub: Link to location
    DOI: 10.5281/zenodo.3862375

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Permalink: https://www.hzdr.de/publications/Publ-31694
Publ.-Id: 31694


Influence of precursor thin-film quality on the structural properties of large-area MoS2 films grown by sulfurization of MoO3 on c-sapphire

Spanková, M.; Sojková, M.; Dobrocka, E.; Hutár, P.; Bodík, M.; Munnik, F.; Hulman, M.; Chromik, S.

In recent years, molybdenum disulfide (MoS2) has been investigated due to its unique electronic, optical, and mechanical properties with a variety of applications. Sulfurization of pre-deposited MoO3 layers is one of the methods of the preparation of large-area MoS2 thin films. The MoO3 layers have been grown on c-sapphire substrates, using two different techniques (rf sputtering, pulsed laser deposition). The films were subsequently annealed in vapors of sulfur at high temperatures what converted them to MoS2 films. The quality of MoS2 is strongly influenced by the properties of the precursor MoO3 layers. The pre-deposited MoO3, as well as the sulfurized MoS2, have been characterized by several techniques including Raman, Rutherford backscattering spectroscopy, atomic force microscopy, scanning electron microscopy, and X-ray diffraction. Here we compare two types of MoS2 films prepared from different MoO3 layers to determine the most suitable MoO3 layer properties providing good quality MoS2 films for future applications.

Keywords: Molybdenum disulfide; Sulfurization; Sputtering; Pulsed laser deposition; Structural properties

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Permalink: https://www.hzdr.de/publications/Publ-31693
Publ.-Id: 31693


Diffraction techniques in nuclear materials

Bergner, F.

The presentation is aimed at introducing diffraction techniques and their applications in the field of structural nuclear materials. After a brief introduction, three selected experimental techniques are presented in more detail. These are X-ray line profile analysis (XLPA), electron backscatter diffraction (EBSD) and small-angle neutron scattering (SANS). XLPA is applied to derive microstructure parameters such as crystallite size, dislocation density and twin probability of a nanostructured high-entropy alloy processed by means of high pressure torsion. EBSD is shown to be useful for the characterization of the bainitic microstructure in terms of subunits of the prior austenite grains and their orientation relationship with the parent phase. As an example for the application of SANS, the effects of neutron flux and neutron fluence on the volume fraction and mean size of irradiation-induced solue atom clusters are characterized.

Keywords: Diffraction; Scattering; Nuclear materials; Irradiation effects

  • Invited lecture (Conferences) (Online presentation)
    European School on Nuclear Material Science, 09.-13.11.2020, Online, Online

Permalink: https://www.hzdr.de/publications/Publ-31692
Publ.-Id: 31692


Frequency- and magnetic-field-dependent properties of ordered magnetic nanoparticle arrangements

Neugebauer, N.; Hache, T.; Elm, M.; Hofmann, D. M.; Heiliger, C.; Schultheiß, H.; Klar, P. J.

We present a frequency and magnetic field dependent investigation of ordered arrangements of 20 nm magnetic
nanoparticles (MNPs) consisting of magnetite (Fe3O4) by employing micro Brillouin light scattering
microscopy. We utilized electron beam lithography to prepare hexagonally arranged, circularly shaped MNPassemblies
consisting of a single layer of MNPs using a variant of the Langmuir-Blodgett technique. By
comparing the results with non-structured, layered superlattices of MNPs, further insight into the influence
of size and geometry of the arrangement on the collective properties is obtained. We show that at low static
external field strengths, two signals occur in frequency dependent measurements for both non-structured and
structured assemblies. Enlarging the static external field strength leads to a sharpening of the main signal,
while the satellite signal decreases in its intensity and increases in its linewidth. The occurrence of multiple
signals at low external field strengths is also confirmed by sweeping the static external field and keeping the
excitation frequency constant. Micromagnetic simulations unravel the origin of the different signals and their
dependence on the static external field strength, enabling an interpretation of the observed characteristics in
terms of different local environments of an MNPs forming the MNP assembly.

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Permalink: https://www.hzdr.de/publications/Publ-31690
Publ.-Id: 31690


Frequency- and magnetic-field-dependent properties of ordered magnetic nanoparticle arrangements

Neugebauer, N.; Hache, T.; Elm, M. T.; Hofmann, D. M.; Heiliger, C.; Schultheiß, H.; Klar, P. J.

We present a frequency and magnetic field dependent investigation of ordered arrangements of 20 nm mag-netic nanoparticles (MNPs) consisting of magnetite (Fe3O4) by employing micro Brillouin light scatteringmicroscopy. We utilized electron beam lithography to prepare hexagonally arranged, circularly shaped MNP-assemblies consisting of a single layer of MNPs using a variant of the Langmuir-Blodgett technique. Bycomparing the results with non-structured, layered superlattices of MNPs, further insight into the influenceof size and geometry of the arrangement on the collective properties is obtained. We show that at low staticexternal field strengths, two signals occur in frequency dependent measurements for both non-structured andstructured assemblies. Enlarging the static external field strength leads to a sharpening of the main signal,while the satellite signal decreases in its intensity and increases in its linewidth. The occurrence of multiplesignals at low external field strengths is also confirmed by sweeping the static external field and keeping theexcitation frequency constant. Micromagnetic simulations unravel the origin of the different signals and theirdependence on the static external field strength, enabling an interpretation of the observed characteristics interms of different local environments of an MNPs forming the MNP assembly.

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Permalink: https://www.hzdr.de/publications/Publ-31689
Publ.-Id: 31689


Optimization of multi-group energy structures for diffusion analyses of sodium-cooled fast reactors assisted by simulated annealing – Part I: methodology demonstration

Di Nora, V. A.; Fridman, E.; Nikitin, E.; Bilodid, Y.; Mikityuk, K.

This study presents an approach to the selection of optimal energy group structures for multi-group nodal diffusion analyses of Sodium-cooled Fast Reactor cores. The goal is to speed up calculations, particularly in transient calculations, while maintaining an acceptable accuracy of the results.
In Part I of the paper, possible time-savings due to collapsing of energy groups are evaluated using 24-group energy structure as a reference. Afterwards, focusing on energy structures with a number of groups leading to significant calculation speedups, optimal grid configurations are identified. Depending on a number of possible energy grid configurations to explore, the optimization is conducted by either a direct search or applying the simulated annealing method. Speedup and optimization studies are performed on a selected case of the Superphénix static neutronic benchmark by using the nodal diffusion DYN3D code. The results demonstrate noticeable improvements in DYN3D performance with a marginal deterioration of the accuracy.

Keywords: Serpent; XS condensation; energy structure optimization; simulated annealing

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Permalink: https://www.hzdr.de/publications/Publ-31688
Publ.-Id: 31688


Radiolabelled Cyclic Bisarylmercury: High Chemical and in vivo Stability for Theranostics

Gilpin, I. M.; Ullrich, M.; Wünsche, T.; Zarschler, K.; Lebeda, O.; Pietzsch, J.; Pietzsch, H.-J.; Walther, M.

We show the synthesis of an in vivo stable mercury compound with functionality suitable for radiopharmaceuticals. The designed cyclic bisarylmercury was based on the water tolerance of organomercurials, higher bond dissociation energy of Hg-Ph to Hg-S, and the experimental evidence that acyclic structures suffer significant cleavage of one of the Hg-R bonds. The bispidine motif was chosen for its in vivo stability, chemical accessibility, and functionalization properties. Radionuclide production results in 197(m)HgCl2(aq), so the desired mercury compound was formed via a water-tolerant organotin transmetallation. The Hg-bispidine compound showed high chemical stability in tests with an excess of sulphur-containing competitors and high in vivo stability, without any observable protein interaction by human serum assay, and good organ clearance demonstrated by biodistribution and SPECT studies in rats. In particular no retention in the kidneys typical of unstable mercury compounds. The natHg analogue allowed full characterization by NMR and HRMS.

Keywords: bispidine; mercury; organomercury; radiopharmaceuticals; radiotheranostics

Permalink: https://www.hzdr.de/publications/Publ-31687
Publ.-Id: 31687


ISAAC - In Situ Animation of Accelerated Computations

Meyer, F.; Widera, R.; Pausch, R.; Matthes, A.; Hübl, A.; Gerber, V.; Zenker, E.; Kosukhin, S.

Many computations like physics or biologists simulations these days run on accelerated hardware like CUDA GPUs or Intel Xeon Phi, which are itself distributed in a big compute cluster communicating over MPI. The goal of ISAAC is to visualize this data without the need to download it to the host while using the high computation speed of the accelerator.

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Permalink: https://www.hzdr.de/publications/Publ-31686
Publ.-Id: 31686


A New Highly Anisotropic Rh-Based Heusler Compound for Magnetic Recording

He, Y.; Fecher, G. H.; Fu, C.; Pan, Y.; Manna, K.; Kroder, J.; Jha, A.; Wang, X.; Hu, Z.; Agrestini, S.; Herrero-Martin, J.; Valvidares, M.; Scurschii, I.; Schnelle, W.; Stamenov, P.; Borrmann, H.; Tjeng, L. H.; Schaefer, R.; Parkin, S. S. P.; Coey, J. M. D.; Felser, C.

The development of high-density magnetic recording media is limited by superparamagnetism in very small ferromagnetic crystals. Hard magnetic materials with strong perpendicular anisotropy offer stability and high recording density. To overcome the difficulty of writing media with a large coercivity, heat-assisted magnetic recording was developed, rapidly heating the media to the Curie temperature Tc before writing, followed by rapid cooling. Requirements are a suitable Tc, coupled with anisotropic thermal conductivity and hard magnetic properties. Here, Rh2CoSb is introduced as a new hard magnet with potential for thin-film magnetic recording. A magnetocrystalline anisotropy of 3.6 MJ m−3 is combined with a saturation magnetization of μ0Ms = 0.52 T at 2 K (2.2 MJ m−3 and 0.44 T at room temperature). The magnetic hardness parameter of 3.7 at room temperature is the highest observed for any rare-earth-free hard magnet. The anisotropy is related to an unquenched orbital moment of 0.42 μB on Co, which is hybridized with neighboring Rh atoms with a large spin–orbit interaction. Moreover, the pronounced temperature dependence of the anisotropy that follows from its Tc of 450 K, together with a thermal conductivity of 20 W m−1 K−1, make Rh2CoSb a candidate for the development of heat-assisted writing with a recording density in excess of 10 Tb in.−2.

Permalink: https://www.hzdr.de/publications/Publ-31685
Publ.-Id: 31685


Superconducting Accelerators as Sources for Intense Secondary Radiations

Wagner, A.

The Helmholtz-Center Dresden-Rossendorf operates a superconducting electron linear accelerator (named ELBE radiation source) as a driver for secondary beams of electromagnetic radiation, neutrons, and positrons. The combination of high-intensity secondary beams, superior timing resolution, and adjustable beam repetition rates allows performing experiments, which are hardly possible using alternative technologies. The facility runs as a dedicated user facility thus serving an international community. Applications range from tunable coherent infra-red radiation from an Free-Electron Laser, coherent super-radiant THz radiation with sub-ps timing, high-energy gamma-rays and neutrons for nuclear physics to secondary positron beams for materials research.
Several recent scientific results will be presented and plans for a successor, the Dresden Advanced Light Infrastructure (DALI), will be shown.

Keywords: ELBE; DALI; positrons; THz; FELBE; TELBE; neutrons; gammas; Felsenkeller; nuclear astrophysics

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  • Lecture (others) (Online presentation)
    Physikalisches Kolloquium der Martin-Luther Universität Halle-Wittenberg, 05.11.2020, Halle/Saale, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-31684
Publ.-Id: 31684


Rare earth minerals and rare-earth mining

Lorenz, T.; Bertau, M.; Möckel, R.

The book chapter is about the geology of rare earth elements, their mineral carrier as well as secondary raw materials.

Permalink: https://www.hzdr.de/publications/Publ-31683
Publ.-Id: 31683


Nanoparticle emission by electronic sputtering of CaF2 single crystals

Alencar, I.; Hatori, M.; Marmitt, G. G.; Trombini, H.; Grande, P. L.; Dias, J. F.; Papaléo, R. M.; Mücklich, A.; Assmann, W.; Toulemonde, M.; Trautmann, C.

Material sputtered from CaF2 single crystals by 180 MeV Au ions impinging at different incidence angles were collected on high-purity amorphous C-coated Cu grids and Si100 wafer catcher surfaces over a broad angular range. These catcher surfaces were characterized complementary by transmission electron microscopy, atomic force microscopy and medium energy ion scattering, revealing the presence of a distribution of partially buried CaF2 nanoparticles in conjunction to a thin layer of deposited CaF2 material. Particle size distributions do not follow simple power laws and depend on the angles of ion incidence and particle detection. It is shown that the particle ejection is directly related to the jet-like component of sputtering, previously observed in ionic crystals, contributing significantly to the total yield. This contribution enhances as the impinging ions approach grazing incidence. Possible scenarios for the emission of particles are discussed in light of these observations.

Keywords: Atomic force microscopyCatcher technique; Nanoparticle; Medium energy ion scattering; Electronic sputtering; Swift heavy ions; Transmission electron microscopy

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Permalink: https://www.hzdr.de/publications/Publ-31682
Publ.-Id: 31682


Cerebral blood flow of the frontal lobe in untreated children with trigonocephaly vs healthy controls: an arterial spin labeling study

de Planque, C. A.; Petr, J.; Gaillard, L.; Mutsaerts, H. J.; van Veelen, M. L. C.; Versnel, S. L.; Dremmen, M.; Mathijssen, I. M. J.

Background: Craniofacial surgery is the standard of treatment for children with moderate to severe trigonocephaly. However, assessing the risk of suboptimal neurodevelopment and added value of surgery is difficult in individual cases. In this study we aim to address the hypothesis that brain development is restricted in trigonocephaly patients by investigating cerebral blood flow in the frontal lobe.
Methods: Between 2018 and 2020, we prospectively included trigonocephaly patients for whom a surgical correction was considered in an MRI study measuring cerebral perfusion with arterial spin labeling (ASL). The mean value of cerebral blood flow (CBF) in the frontal lobe was calculated for each subject and compared between the trigonocephaly patients and healthy controls.
Results: MRI scans of 36 trigonocephaly patients (median age 0.5y, IQR 0.3, 11 females) were included and compared with 16 controls without cerebral pathology (median age 0.83y, IQR 0.56, 10 females). The mean CBF values in the frontal lobe of the trigonocephaly patients (73.0 ml/100g/min) did not appear to be significantly different in comparison with controls (70.5 ml/100g/min, p = 0.6479). The superior, middle, and inferior part of the frontal lobe showed no significant differences either.
Conclusions: Before surgery, the frontal lobe of trigonocephaly patients aged under 18 months old has a normal CBF. In addition to the previously reported very low prevalence of papilledema or impaired skull growth, this finding further supports our hypothesis that craniofacial surgery for trigonocephaly is rarely indicated for signs of raised intracranial pressure.

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Permalink: https://www.hzdr.de/publications/Publ-31681
Publ.-Id: 31681


Pictures worth more than a thousand words: prediction of survival in medulloblastoma patients

Rabasco Meneghetti, A.; Zwanenburg, A.; Löck, S.

In this invited comment we discuss the results of the manuscript of Yan et al. EbioMedicine, with title "Incremental prognostic value and underlying biological pathways of radiomics patterns in medulloblastoma"

Permalink: https://www.hzdr.de/publications/Publ-31680
Publ.-Id: 31680


Definition and validation of a radiomics signature for loco-regional tumour control in patients with locally advanced head and neck squamous cell carcinoma

Rabasco Meneghetti, A.; Zwanenburg, A.; Leger, S.; Leger, K.; Troost, E. G. C.; Linge, A.; Lohaus, F.; Schreiber, A.; Kalinauskaite, G.; Tinhofer, I.; Guberina, N.; Guberina, M.; Balermpas, P.; von der Grün, J.; Ganswindt, U.; Belka, C.; Peeken, J. C.; Combs, S. E.; Böke, S.; Zips, D.; Krause, M.; Baumann, M.; Löck, S.

Purpose: To develop and validate a CT-based radiomics signature for the prognosis of loco-regional tumour control (LRC) in patients with locally advanced head and neck squamous cell carcinoma (HNSCC) treated by primary radiochemotherapy (RCTx) based on retrospective data from 6 partner sites of the German Cancer Consortium – Radiation Oncology Group (DKTK-ROG).
Material and methods: Pre-treatment CT images of 318 patients with locally advanced HNSCC were collected. Four-hundred forty-six features were extracted from each primary tumour volume and then filtered through stability analysis and clustering. First, a baseline signature was developed from demographic and tumour-associated clinical parameters. This signature was then supplemented by CT imaging features. A final signature was derived using repeated 3-fold cross-validation on the discovery cohort. Performance in external validation was assessed by the concordance index (C-Index). Furthermore, calibration and patient stratification in groups with low and high risk for loco-regional recurrence were analysed.
Results: For the clinical baseline signature, only the primary tumour volume was selected. The final signature combined the tumour volume with two independent radiomics features. It achieved moderately good discriminatory performance (C-Index [95% confidence interval]: 0.66 [0.55-0.75]) on the validation cohort along with significant patient stratification (p=0.005) and good calibration.
Conclusion: We identified and validated a clinical-radiomics signature for LRC of locally advanced HNSCC using a multi-centric retrospective dataset. Prospective validation will be performed on the primary cohort of the HNprädBio trial of the DKTK-ROG once follow-up is completed.

Keywords: HNSCC; Radiomics; Validation; Biomarker; Machine Learning; Loco-regional control

Permalink: https://www.hzdr.de/publications/Publ-31679
Publ.-Id: 31679


Voltage‐driven motion of nitrogen ions: a new paradigm for magneto‐ionics

de Rojas, J.; Quintana, A.; Lopeandia, A.; Salguero, J.; Muñiz, B.; Ibrahim, F.; Chshiev, M.; Nicolenco, A.; Liedke, M. O.; Butterling, M.; Wagner, A.; Sireus, V.; Abad, L.; Jensen, C.; Liu, K.; Nogues, J.; Costa-Krämer, J.; Sort, J.; Menéndez, E.

Magneto‐ionics, understood as voltage‐driven ion transport in magnetic materials, has largely relied on controlled migration of oxygen ions. Here, we demonstrate room‐temperature voltagedriven nitrogen transport (i.e., nitrogen magneto‐ionics) by electrolyte‐gating of a CoN film.
Nitrogen magneto‐ionics in CoN is compared to oxygen magneto‐ionics in Co3O4. Both materials are nanocrystalline (face‐centered‐cubic structure) and show reversible voltage‐driven ON‐OFF ferromagnetism. In contrast to oxygen, nitrogen transport occurs uniformly creating a plane‐wavelike migration front, without assistance of diffusion channels. Remarkably, nitrogen magnetoionics requires lower threshold voltages and exhibits enhanced rates and cyclability. This is due to the lower activation energy for ion diffusion and the lower electronegativity of nitrogen compared to oxygen. These results may open new avenues in applications such as brain‐inspired computing or iontronics in general.

Keywords: positron annihilation spectroscopy; magneto-ionics; positron annihilation lifetime spectroscopy; defetcs; nitrogen; Co

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Permalink: https://www.hzdr.de/publications/Publ-31678
Publ.-Id: 31678


Lithium-assisted Exfoliation and Photoelectrocatalytic Water Splitting of 2D Palladium Thiophosphate

Wu, B.; Kempt, R.; Kovalska, E.; Luxa, J.; Kuc, A. B.; Heine, T.; Sofer, Z.

Efficient photoelectrocatalytic (PEC) water splitting could be the solution for environmental and energy problems on planet Earth. Here, we explore 2D palladium thiophosphate Pd3(PS4)2, which is a promising photocatalyst absorbing light in the visible range. We obtain a few-layer Pd3(PS4)2 through lithium-assisted exfoliation from the bulk phase and characterize it employing Raman spectroscopy, XPS, AFM, and STM combined with DFT calculations. The measured band gap for as-obtained few-layer Pd3(PS4)2 is 2.57 eV (indirect) and its band edges span the electrochemical potentials of the hydrogen and oxygen evolution reactions. The performance in the water-splitting reaction is studied under acidic, neutral, and alkaline conditions under violet irradiation at 420 nm. 2D palladium phosphochalcogenides semiconductor with bifunctional electrocatalytic and photoelectrocatalytic properties. Our results show competitive performance compared with industrial Pt/C catalysts for solar-driven water splitting under acidic and alkaline conditions.

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Permalink: https://www.hzdr.de/publications/Publ-31677
Publ.-Id: 31677


TiOx/Pt3Ti(111) Surface-Directed Formation of Electronically Responsive, Supramolecular Assemblies of Tungsten Oxide Clusters

Moors, M.; An, Y.; Kuc, A. B.; Monakhov, K.

Highly ordered titanium oxide films grown on the Pt3Ti(111) alloy surface have been utilized for the controlled immobilization and the tip-induced electric field triggered electronic manipulation of nanoscopic W3O9 clusters. Depending on the operating conditions two different stable oxide phases z’-TiOx and w’-TiOx were produced. These phases show a strong effect on the adsorption characteristics and reactivity of W3O9 clusters that are formed as a result of thermal evaporation of WO3 powder on the complex TiOx/Pt3Ti(111) surfaces under ultra-high vacuum conditions. The physisorbed tritungsten nonaoxides were found as isolated single units located on metallic attraction points or as supramolecular self-assemblies with a W3O9-capped hexagonal scaffold of W3O9 units. By applying the scanning tunneling microscopy to the W3O9(W3O9)6 structures individual units undergo a tip induced reduction to W3O8. At elevated temperatures agglomeration and the growth of large WO3 islands, which thickness is strongly limited to a maximum of two unit cells, is observed. The findings boost progress toward the template-directed nucleation, growth, networking and charge state-manipulation of functional molecular nanostructures at surfaces using operando techniques.

Permalink: https://www.hzdr.de/publications/Publ-31676
Publ.-Id: 31676


Tuning valleys and wave functions of van der Waals heterostructures by varying the number of layers: A first-principles study

Ramzan, M. S.; Kunstmann, J.; Kuc, A. B.

In van der Waals heterostructures of two-dimensional transition-metal dichalcogenides (2D TMDCs) electron and hole states are spatially localized in different layers forming long-lived interlayer excitons. Here, we have investigated, from first principles, the influence of additional electron or hole layers on the electronic properties of a MoS2/WSe2 heterobilayer (HBL), which is a direct band gap material. Additional layers modify the interlayer hybridization, mostly affecting the quasiparticle energy and real-space extend of hole states at the G and electron states at the Q valleys. For a sufficient number of additional layers, the band edges move from K to Q or G, respectively. Adding electron layers to the HBL leads to more delocalized Q states, while G states do not extend much beyond the HBL, even when more hole layers are added. These results suggest a simple and yet powerful way to tune band edges and the real-space extend of the electron and hole wave function in TMDC heterostructures, strongly affecting the lifetime and dynamics of interlayer excitons.

Permalink: https://www.hzdr.de/publications/Publ-31675
Publ.-Id: 31675


The dithiol-dithione tautomerism of 2,3-pyrazinedithiol in the synthesis of copper and silver coordination compounds

Henfling, S.; Kempt, R.; Klose, J.; Kuc, A. B.; Kersting, B.; Krautscheid, H.

A promising strategy for new electrically conductive coordination polymers is the combination of d10 metal ions, which tolerate short metal···metal distances, with dithiolene linkers, known for their “non-innocent” redox behavior. This study explores the coordination chemistry of 2,3-pyrazinedithiol (H2pdt) towards Cu+ and Ag+ ions, highlighting similarities and differences. The synthetic approach, starting with the fully protonated ligand, allowed the isolation of a homoleptic bis(dithiolene) complex with formal CuI atoms, [Cu(H2pdt)2]Cl (1). This complex was further transformed to a one-dimensional coordination polymer with short metal···metal distances, 1D[Cu(Hpdt)] (2Cu). The larger Ag+ ion directly built up a very similar coordination polymer 1D[Ag(Hpdt)] (2Ag), without any appearance of an intermediate metal complex. The coordination polymer 1D[Cu(H2pdt)I] (4), like complex 1, bears fully protonated H2pdt ligands in their dithione form. Upon heating, both compounds underwent auto-oxidation coupled with a dehydrogenation of the ligand to form the open shell neutral copper(II) complex [Cu(Hpdt)2] (3) and the coordination polymer 1D[Cu2I2(Hpdt)(H2pdt)] (5), respectively. For all presented compounds, crystal structures are discussed in-depth. Furthermore, properties of 1, 3, as well as of the three one-dimensional coordination polymers 2Ag, 2Cu and 4, were investigated by UV-Vis-NIR spectroscopy, cyclic voltammetry, and variable temperature magnetic susceptibility, and DC-conductivity measurements. The experimental results are compared and discussed with the aid of DFT simulations.

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